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RFC 1327 - Mapping between X.400(1988) / ISO 10021 and RFC 822


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Network Working Group                                S. Hardcastle-Kille
Request for Comments: 1327                     University College London
Obsoletes: RFCs 987, 1026, 1138, 1148                           May 1992
Updates: RFC 822

          Mapping between X.400(1988) / ISO 10021 and RFC 822

Status of this Memo

   This RFC specifies an IAB standards track protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

Abstract

   This document describes a set of mappings which will enable
   interworking between systems operating the CCITT X.400 1988)
   Recommendations on Message Handling Systems / ISO IEC 10021 Message
   Oriented Text Interchange Systems (MOTIS) [CCITT/ISO88a], and systems
   using the RFC 822 mail protocol [Crocker82a] or protocols derived
   from RFC 822.  The approach aims to maximise the services offered
   across the boundary, whilst not requiring unduly complex mappings.
   The mappings should not require any changes to end systems. This
   document is a revision based on RFCs 987, 1026, 1138, and 1148
   [Kille86a,Kille87a] which it obsoletes.

   This document specifies a mapping between two protocols.  This
   specification should be used when this mapping is performed on the
   DARPA Internet or in the UK Academic Community.  This specification
   may be modified in the light of implementation experience, but no
   substantial changes are expected.

Table of Contents

   1          - Overview ......................................    3
   1.1        - X.400 .........................................    3
   1.2        - RFC 822 .......................................    3
   1.3        - The need for conversion .......................    4
   1.4        - General approach ..............................    4
   1.5        - Gatewaying Model ..............................    5
   1.6        - X.400 (1984) ..................................    8
   1.7        - Compatibility with previous versions ..........    8
   1.8        - Aspects not covered ...........................    8
   1.9        - Subsetting ....................................    9
   1.10       - Document Structure ............................    9

   1.11       - Acknowledgements ..............................    9
   2          - Service Elements ..............................   10
   2.1        - The Notion of Service Across a Gateway ........   10
   2.2        - RFC 822 .......................................   11
   2.3        - X.400 .........................................   15
   3          - Basic Mappings ................................   24
   3.1        - Notation ......................................   24
   3.2        - ASCII and IA5 .................................   26
   3.3        - Standard Types ................................   26
   3.4        - Encoding ASCII in Printable String ............   28
   4          - Addressing ....................................   30
   4.1        - A textual representation of MTS.ORAddress .....   30
   4.2        - Basic Representation ..........................   31
   4.3        - EBNF.822-address <-> MTS.ORAddress ............   36
   4.4        - Repeated Mappings .............................   48
   4.5        - Directory Names ...............................   50
   4.6        - MTS Mappings ..................................   50
   4.7        - IPMS Mappings .................................   55
   5          - Detailed Mappings .............................   59
   5.1        - RFC 822 -> X.400 ..............................   59
   5.2        - Return of Contents ............................   67
   5.3        - X.400 -> RFC 822 ..............................   67
   Appendix A - Mappings Specific to SMTP .....................   91
   Appendix B - Mappings specific to the JNT Mail .............   91
   1          - Introduction ..................................   91
   2          - Domain Ordering ...............................   91
   3          - Addressing ....................................   91
   4          - Acknowledge-To:  ..............................   91
   5          - Trace .........................................   92
   6          - Timezone specification ........................   92
   7          - Lack of 822-MTS originator specification ......   92
   Appendix C - Mappings specific to UUCP Mail ................   93
   Appendix D - Object Identifier Assignment ..................   94
   Appendix E - BNF Summary ...................................   94
   Appendix F - Format of address mapping tables ..............  101
   1          - Global Mapping Information ....................  101
   2          - Syntax Definitions ............................  102
   3          - Table Lookups .................................  103
   4          - Domain -> O/R Address format ..................  104
   5          - O/R Address -> Domain format ..................  104
   6          - Domain -> O/R Address of Gateway table ........  104
   Appendix G - Mapping with X.400(1984) ......................  105
   Appendix H - RFC 822 Extensions for X.400 access ...........  106
   Appendix I - Conformance ...................................  106
   Appendix J - Change History: RFC 987, 1026, 1138, 1148 .....  107
   1          - Introduction ..................................  108
   2          - Service Elements ..............................  108
   3          - Basic Mappings ................................  108

   4          - Addressing ....................................  108
   5          - Detailed Mappings .............................  109
   6          - Appendices ....................................  109
   Appendix K - Change History: RFC 1148 to this Document .....  109
   1          - General .......................................  109
   2          - Basic Mappings ................................  110
   3          - Addressing ....................................  110
   4          - Detailed Mappings .............................  110
   5          - Appendices ....................................  110
   References .................................................  111
   Security Considerations ....................................  113
   Author's Address ...........................................  113

Chapter 1 -- Overview

1.1.  X.400

   This document relates to the CCITT 1988 X.400 Series Recommendations
   / ISO IEC 10021 on the Message Oriented Text Interchange Service
   (MOTIS).  This ISO/CCITT standard is referred to in this document as
   "X.400", which is a convenient shorthand.  Any reference to the 1984
   CCITT Recommendations will be explicit.  X.400 defines an
   Interpersonal Messaging System (IPMS), making use of a store and
   forward Message Transfer System.  This document relates to the IPMS,
   and not to wider application of X.400.  It is expected that X.400
   will be implemented very widely.

1.2. RFC 822

   RFC 822 evolved as a messaging standard on the DARPA (the US Defense
   Advanced Research Projects Agency) Internet.  It specifies and end to
   end message format.  It is used in conjunction with a number of
   different message transfer protocol environments.

   SMTP Networks
       On the DARPA Internet and other TCP/IP networks, RFC 822 is
       used in conjunction with two other standards: RFC 821, also
       known as Simple Mail Transfer Protocol (SMTP) [Postel82a],
       and RFC 920 which is a Specification for domains and a
       distributed name service [Postel84a].

   UUCP Networks
       UUCP is the UNIX to UNIX CoPy protocol, which is usually
       used over dialup telephone networks to provide a simple
       message transfer mechanism.  There are some extensions to
       RFC 822, particularly in the addressing.  They use domains
       which conform to RFC 920, but not the corresponding domain
       nameservers [Horton86a].

   Bitnet
       Some parts of Bitnet and related networks use RFC 822
       related protocols, with EBCDIC encoding.

   JNT Mail Networks
       A number of X.25 networks, particularly those associated
       with the UK Academic Community, use the JNT (Joint Network
       Team) Mail Protocol, also known as Greybook [Kille84a].
       This is used with domains and name service specified by the
       JNT NRS (Name Registration Scheme) [Larmouth83a].

   The mappings specified here are appropriate for all of these
   networks.

1.3.  The need for conversion

   There is a large community using RFC 822 based protocols for mail
   services, who will wish to communicate with users of the IPMS
   provided by X.400 systems.  This will also be a requirement in cases
   where communities intend to make a transition to use of an X.400
   IPMS, as conversion will be needed to ensure a smooth service
   transition.  It is expected that there will be more than one gateway,
   and this specification will enable them to behave in a consistent
   manner.  Note that the term gateway is used to describe a component
   performing the protocol mappings between RFC 822 and X.400.  This is
   standard usage amongst mail implementors, but should be noted
   carefully by transport and network service implementors.

   Consistency between gateways is desirable to provide:

   1.   Consistent service to users.

   2.   The best service in cases where a message passes through
        multiple gateways.

1.4.  General approach

   There are a number of basic principles underlying the details of the
   specification.  These principles are goals, and are not achieved in
   all aspects of the specification.

   1.   The specification should be pragmatic.  There should not be
        a requirement for complex mappings for "Academic" reasons.
        Complex mappings should not be required to support trivial
        additional functionality.

   2.   Subject to 1), functionality across a gateway should be as
        high as possible.

   3.   It is always a bad idea to lose information as a result of
        any transformation.  Hence, it is a bad idea for a gateway
        to discard information in the objects it processes.  This
        includes requested services which cannot be fully mapped.

   4.   All mail gateways actually operate at exactly one level
        above the layer on which they conceptually operate.  This
        implies that the gateway must not only be cognisant of the
        semantics of objects at the gateway level, but also be
        cognisant of higher level semantics.  If meaningful
        transformation of the objects that the gateway operates on
        is to occur, then the gateway needs to understand more than
        the objects themselves.

   5.   Subject to 1), the specification should be reversible.  That
        is, a double transformation should bring you back to where
        you started.

1.5.  Gatewaying Model

1.5.1.  X.400

   X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7,
   [CCITT/ISO88b] which comprises of three basic services:

   1.   Origination

   2.   Reception

   3.   Management

   Management is a local interaction between the user and the IPMS, and
   is therefore not relevant to gatewaying.  The first two services
   consist of operations to originate and receive the following two
   objects:

   1.   IPM (Interpersonal Message). This has two components: a
        heading, and a body.  The body is structured as a sequence
        of body parts, which may be basic components (e.g., IA5
        text, or G3 fax), or IP Messages.  The heading consists of
        fields containing end to end user information, such as
        subject, primary recipients (To:), and importance.

   2.   IPN (Inter Personal Notification).  A notification  about
        receipt of a given IPM at the UA level.

   The Origination service also allows for origination of a probe, which
   is an object to test whether a given IPM could be correctly received.

   The Reception service also allows for receipt of Delivery Reports
   DR), which indicate delivery success or failure.

   These IPMS Services utilise the Message Transfer (MT) Abstract
   Service [CCITT/ISO88c].  The MT Abstract Service provides the
   following three basic services:

   1.   Submission (used by IPMS Origination)

   2.   Delivery (used by IPMS Reception)

   3.   Administration (used by IPMS Management)

   Administration is a local issue, and so does not affect this
   standard.  Submission and delivery relate primarily to the MTS
   Message (comprising Envelope and Content), which carries an IPM or
   IPN (or other uninterpreted contents).  There is also an Envelope,
   which includes an ID, an originator, and a list of recipients.
   Submission also includes the probe service, which supports the IPMS
   Probe. Delivery also includes Reports, which indicate whether a given
   MTS Message has been delivered or not.

   The MTS is REFINED into the MTA (Message Transfer Agent) Service,
   which defines the interaction between MTAs, along with the procedures
   for distributed operation.  This service provides for transfer of MTS
   Messages, Probes, and Reports.

1.5.2.  RFC 822

   RFC 822 is based on the assumption that there is an underlying
   service, which is here called the 822-MTS service.  The 822-MTS
   service provides three basic functions:

   1.   Identification of a list of recipients.

   2.   Identification of an error return address.

   3.   Transfer of an RFC 822 message.

   It is possible to achieve 2) within the RFC 822 header.  Some 822-MTS
   protocols, in particular SMTP, can provide additional functionality,
   but as these are neither mandatory in SMTP, nor available in other
   822-MTS protocols, they are not considered here.  Details of aspects
   specific to two 822-MTS protocols are given in Appendices B and C.
   An RFC 822 message consists of a header, and content which is
   uninterpreted ASCII text.  The header is divided into fields, which
   are the protocol elements.  Most of these fields are analogous to P2
   heading fields, although some are analogous to MTS Service Elements

   or MTA Service Elements.

1.5.3.  The Gateway

   Given this functional description of the two services, the functional
   nature of a gateway can now be considered.  It would be elegant to
   consider the 822-MTS service mapping onto the MTS Service Elements
   and RFC 822 mapping onto an IPM, but reality just does not fit.
   Another elegant approach would be to treat this document as the
   definition of an X.400 Access Unit (AU).  Again, reality does not
   fit.  It is necessary to consider that the IPM format definition, the
   IPMS Service Elements, the MTS Service Elements, and MTA Service
   Elements on one side are mapped into RFC 822 + 822-MTS on the other
   in a slightly tangled manner.  The details of the tangle will be made
   clear in Chapter 5.  Access to the MTA Service Elements is minimised.

   The following basic mappings are thus defined.  When going from RFC
   822 to X.400, an RFC 822 message and the associated 822-MTS
   information is always mapped into an IPM (MTA, MTS, and IPMS
   Services).  Going from X.400 to RFC 822, an RFC 822 message and the
   associated 822-MTS information may be derived from:

   1.   A Report (MTA, and MTS Services)

   2.   An IPN (MTA, MTS, and IPMS services)

   3.   An IPM (MTA, MTS, and IPMS services)

   Probes (MTA Service) must be processed by the gateway, as discussed
   in Chapter 5.  MTS Messages containing Content Types other than those
   defined by the IPMS are not mapped by the gateway, and should be
   rejected at the gateway.

1.5.4.  Repeated Mappings

   The primary goal of this specification is to support single mappings,
   so that X.400 and RFC 822 users can communicate with maximum
   functionality.

   The mappings specified here are designed to work where a message
   traverses multiple times between X.400 and RFC 822. This is often
   essential, particularly in the case of distribution lists.  However,
   in general, this will lead to a level of service which is the lowest
   common denominator (approximately the services offered by RFC 822).

   Some RFC 822 networks may wish to use X.400 as an interconnection
   mechanism (typically for policy reasons), and this is fully
   supported.

   Where an X.400 messages transfers to RFC 822 and then back to X.400,
   there is no expectation of X.400 services which do not have an
   equivalent service in standard RFC 822 being preserved - although
   this may be possible in some cases.

1.6.  X.400 (1984)

   Much of this work is based on the initial specification of RFC 987
   and in its addendum RFC 1026, which defined a mapping between
   X.400(1984) and RFC 822.  A basic decision is that the mapping
   defined in this document is to the full 1988 version of X.400, and
   not to a 1984 compatible subset. New features of X.400(1988) can be
   used to provide a much cleaner mapping than that defined in RFC 987.
   This is important, to give good support to communities which will
   utilise full X.400 at an early date.   To interwork with 1984
   systems, Appendix G shall be followed.

   If a message is being transferred to an X.400(1984) system by way of
   X.400(1988) MTA it will give a slightly better service to follow the
   rules of Appendix G.

1.7.  Compatibility with previous versions

   The changes between this and older versions of the document are given
   in Appendices I and J.    These are RFCs 987, 1026, 1138, and 1148.
   This document is a revision of RFC 1148 [Kille90a].  As far as
   possible, changes have been made in a compatible fashion.

1.8.  Aspects not covered

   There have been a number of cases where RFC 987 was used in a manner
   which was not intended.  This section is to make clear some
   limitations of scope.  In particular, this specification does not
   specify:

   -   Extensions of RFC 822 to provide access to all X.400
       services

   -    X.400 user interface definition

   -    Mapping X.400 to extended versions of RFC 822, with support
        for multimedia content.

   The first two of these are really coupled.  To map the X.400
   services, this specification defines a number of extensions to RFC
   822.  As a side effect, these give the 822 user access to SOME X.400
   services.  However, the aim on the RFC 822 side is to preserve
   current service, and it is intentional that access is not given to

   all X.400 services.  Thus, it will be a poor choice for X.400
   implementors to use RFC 987(88) as an interface - there are too many
   aspects of X.400 which cannot be accessed through it.  If a text
   interface is desired, a specification targeted at X.400, without RFC
   822 restrictions, would be more appropriate.  Some optional and
   limited extensions in this area have proved useful, and are defined
   in Appendix H.

1.9.  Subsetting

   This proposal specifies a mapping which is appropriate to preserve
   services in existing RFC 822 communities.  Implementations and
   specifications which subset this specification are strongly
   discouraged.

1.10.  Document Structure

   This document has five chapters:

   1.   Overview - this chapter.

   2.   Service Elements - This describes the (end user) services
        mapped by a gateway.

   3.   Basic mappings - This describes some basic notation used in
        Chapters 3-5, the mappings between character sets, and some
        fundamental protocol elements.

   4.   Addressing - This considers the mapping between X.400 O/R
        names and RFC 822 addresses, which is a fundamental gateway
        component.

   5.   Detailed Mappings - This describes the details of all other
        mappings.

   There are also eleven appendices.

   WARNING:
        THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
        IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND
        X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
        YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

1.11.  Acknowledgements

   The work in this specification was substantially based on RFC 987 and
   RFC 1148, which had input from many people, who are credited in the
   respective documents.

   A number of comments from people on RFC 1148 lead to this document.
   In particular, there were comments and suggestions from:  Maurice
   Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen (X-Tel); Jim
   Craigie (JNT); Ella Gardener (MITRE); Christian Huitema (Inria); Erik
   Huizer (SURFnet); Neil Jones DEC); Ignacio Martinez (IRIS); Julian
   Onions (X-Tel); Simon Poole (SWITCH); Clive Roberts (Data General);
   Pete Vanderbilt SUN); Alan Young (Concurrent).

Chapter 2 - Service Elements

   This chapter considers the services offered across a gateway built
   according to this specification.  It gives a view of the
   functionality provided by such a gateway for communication with users
   in the opposite domain.  This chapter considers service mappings in
   the context of SINGLE transfers only, and not repeated mappings
   through multiple gateways.

2.1.  The Notion of Service Across a Gateway

   RFC 822 and X.400 provide a number of services to the end user.  This
   chapter describes the extent to which each service can be supported
   across an X.400 <-> RFC 822 gateway.  The cases considered are single
   transfers across such a gateway, although the problems of multiple
   crossings are noted where appropriate.

2.1.1.  Origination of Messages

   When a user originates a message, a number of services are available.
   Some of these imply actions (e.g., delivery to a recipient), and some
   are insertion of known data (e.g., specification of a subject field).
   This chapter describes, for each offered service, to what extent it
   is supported for a recipient accessed through a gateway.  There are
   three levels of support:

   Supported
        The corresponding protocol elements map well, and so the
        service can be fully provided.

   Not Supported
        The service cannot be provided, as there is a complete
        mismatch.

   Partial Support
        The service can be partially fulfilled.

   In the first two cases, the service is simply marked as Supported" or
   "Not Supported".  Some explanation may be given if there are
   additional implications, or the (non) support is not intuitive.  For

   partial support, the level of partial support is summarised.  Where
   partial support is good,  this will be described by a phrase such as
   "Supported by use of.....".  A common case of this is where the
   service is mapped onto a non- standard service on the other side of
   the gateway, and this would have lead to support if it had been a
   standard service.  In many cases, this is equivalent to support.  For
   partial support, an indication of the mechanism is given, in order to
   give a feel for the level of support provided.  Note that this is not
   a replacement for Chapter 5, where the mapping is fully specified.

   If a service is described as supported, this implies:

   -    Semantic correspondence.

   -    No (significant) loss of information.

   -    Any actions required by the service element.

   An example of a service gaining full support: If an RFC 822
   originator specifies a Subject:  field, this is considered to be
   supported, as an X.400 recipient will get a subject indication.

   In many cases, the required action will simply be to make the
   information available to the end user.  In other cases, actions may
   imply generating a delivery report.

   All RFC 822 services are supported or partially supported for
   origination.  The implications of non-supported X.400 services is
   described under X.400.

2.1.2.  Reception of Messages

   For reception, the list of service elements required to support this
   mapping is specified.  This is really an indication of what a
   recipient might expect to see in a message which has been remotely
   originated.

2.2.  RFC 822

   RFC 822 does not explicitly define service elements, as distinct from
   protocol elements.  However, all of the RFC 822 header fields, with
   the exception of trace, can be regarded as corresponding to implicit
   RFC 822 service elements.

2.2.1.  Origination in RFC 822

   A mechanism of mapping, used in several cases, is to map the RFC 822
   header into a heading extension in the IPM (InterPersonal Message).

   This can be regarded as partial support, as it makes the information
   available to any X.400 implementations which are interested in these
   services. Communities which require significant RFC 822 interworking
   are recommended to require that their X.400 User Agents are able to
   display these heading extensions.  Support for the various service
   elements (headers) is now listed.

   Date:
        Supported.

   From:
        Supported.  For messages where there is also a sender field,
        the mapping is to "Authorising Users Indication", which has
        subtly different semantics to the general RFC 822 usage of
        From:.

   Sender:
        Supported.

   Reply-To:
        Supported.

   To:  Supported.

   Cc:  Supported.

   Bcc: Supported.

   Message-Id:
        Supported.

   In-Reply-To:
        Supported, for a single reference.  Where multiple
        references are given, partial support is given by mapping to
        "Cross Referencing Indication".  This gives similar
        semantics.

   References:
        Supported.

   Keywords:
        Supported by use of a heading extension.

   Subject:
        Supported.

   Comments:
        Supported by use of an extra body part.

   Encrypted:
        Supported by use of a heading extension.

   Resent-*
        Supported by use of a heading extension.  Note that
        addresses in these fields are mapped onto text, and so are
        not accessible to the X.400 user as addresses.  In
        principle, fuller support would be possible by mapping onto
        a forwarded IP Message, but this is not suggested.

   Other Fields
        In particular X-* fields, and "illegal" fields in common
        usage (e.g., "Fruit-of-the-day:") are supported by use of
        heading extensions.

2.2.2.  Reception by RFC 822

   This considers reception by an RFC 822 User Agent of a message
   originated in an X.400 system and transferred across a gateway.  The
   following standard services (headers) may be present in such a
   message:

   Date:

   From:

   Sender:

   Reply-To:

   To:

   Cc:

   Bcc:

   Message-Id:

   In-Reply-To:

   References:

   Subject:

   The following non-standard services (headers) may be present.  These
   are defined in more detail in Chapter 5 (5.3.4, 5.3.6, 5.3.7):

   Autoforwarded:

   Content-Identifier:

   Conversion:

   Conversion-With-Loss:

   Delivery-Date:

   Discarded-X400-IPMS-Extensions:

   Discarded-X400-MTS-Extensions:

   DL-Expansion-History:

   Deferred-Delivery:

   Expiry-Date:

   Importance:

   Incomplete-Copy:

   Language:

   Latest-Delivery-Time:

   Message-Type:

   Obsoletes:

   Original-Encoded-Information-Types:

   Originator-Return-Address:

   Priority:

   Reply-By:

   Requested-Delivery-Method:

   Sensitivity:

   X400-Content-Type:

   X400-MTS-Identifier:

   X400-Originator:

   X400-Received:

   X400-Recipients:

2.3.  X.400

2.3.1.  Origination in X.400

   When mapping services from X.400 to RFC 822 which are not supported
   by RFC 822, new RFC 822 headers are defined.  It is intended that
   these fields will be registered, and that co- operating RFC 822
   systems may use them.  Where these new fields are used, and no system
   action is implied, the service can be regarded as being partially
   supported.  Chapter 5 describes how to map X.400 services onto these
   new headers.  Other elements are provided, in part, by the gateway as
   they cannot be provided by RFC 822.

   Some service elements are marked N/A (not applicable).  There are
   five cases, which are marked with different comments:

   N/A (local)
        These elements are only applicable to User Agent / Message
        Transfer Agent interaction and so they cannot apply to RFC
        822 recipients.

   N/A (PDAU)
        These service elements are only applicable where the
        recipient is reached by use of a Physical Delivery Access
        Unit (PDAU), and so do not need to be mapped by the gateway.

   N/A (reception)
        These services  are only applicable for reception.

   N/A (prior)
        If requested, this service must be performed prior to the
        gateway.

   N/A (MS)
        These services are only applicable to Message Store (i.e., a
        local service).

   Finally, some service elements are not supported.  In particular, the
   new security services are not mapped onto RFC 822.  Unless otherwise
   indicated, the behaviour of service elements marked as not supported
   will depend on the criticality marking supplied by the user.  If the
   element is marked as critical for transfer or delivery, a non-

   delivery notification will be generated.  Otherwise, the service
   request will be ignored.

2.3.1.1.  Basic Interpersonal Messaging Service

   These are the mandatory IPM services as listed in Section 19.8 of
   X.400 / ISO/IEC 10021-1, listed here in the order given. Section 19.8
   has cross references to short definitions of each service.

   Access management
        N/A (local).

   Content Type Indication
        Supported by a new RFC 822 header (Content-Type:).

   Converted Indication
        Supported by a new RFC 822 header (X400-Received:).

   Delivery Time Stamp Indication
        N/A (reception).

   IP Message Identification
        Supported.

   Message Identification
        Supported, by use of a new RFC 822 header
        (X400-MTS-Identifier).  This new header is required, as
        X.400 has two message-ids whereas RFC 822 has only one (see
        previous service).

   Non-delivery Notification
        Not supported, although in general an RFC 822 system will
        return error reports by use of IP messages.  In other
        service elements, this pragmatic result can be treated as
        effective support of this service element.

   Original Encoded Information Types Indication
        Supported as a new RFC 822 header
        (Original-Encoded-Information-Types:).

   Submission Time Stamp Indication
        Supported.

   Typed Body
        Some types supported.  IA5 is fully supported.
        ForwardedIPMessage is supported, with some loss of
        information.  Other types get some measure of support,
        dependent on X.400 facilities for conversion to IA5.  This

        will only be done where content conversion is not
        prohibited.

   User Capabilities Registration
        N/A (local).

2.3.1.2.  IPM Service Optional User Facilities

   This section describes support for the optional (user selectable) IPM
   services as listed in Section 19.9 of X.400 / ISO/IEC 10021- 1,
   listed here in the order given.  Section 19.9 has cross references to
   short definitions of each service.

   Additional Physical Rendition
        N/A (PDAU).

   Alternate Recipient Allowed
        Not supported.  There is no RFC 822 service equivalent to
        prohibition of alternate recipient assignment (e.g., an RFC
        822 system may freely send an undeliverable message to a
        local postmaster).  Thus, the gateway cannot prevent
        assignment of alternative recipients on the RFC 822 side.
        This service really means giving the user control as to
        whether or not an alternate recipient is allowed. This
        specification requires transfer of messages to RFC 822
        irrespective of this service request, and so this service is
        not supported.

   Authorising User's Indication
        Supported.

   Auto-forwarded Indication
        Supported as new RFC 822 header (Auto-Forwarded:).

   Basic Physical Rendition
        N/A (PDAU).

   Blind Copy Recipient Indication
        Supported.

   Body Part Encryption Indication
        Supported by use of a new RFC 822 header
        (Original-Encoded-Information-Types:), although in most
        cases it will not be possible to map the body part in
        question.

   Content Confidentiality
        Not supported.

   Content Integrity
        Not supported.

   Conversion Prohibition
        Supported.  In this case, only messages with IA5 body parts,
        other body parts which contain only IA5, and Forwarded IP
        Messages (subject recursively to the same restrictions),
        will be mapped.

   Conversion Prohibition in Case of Loss of Information
        Supported.

   Counter Collection
        N/A (PDAU).

   Counter Collection with Advice
        N/A (PDAU).

   Cross Referencing Indication
        Supported.

   Deferred Delivery
        N/A (prior).  This service should always be provided by the
        MTS prior to the gateway.  A new RFC 822 header
        Deferred-Delivery:) is provided to transfer information on
        this service to the recipient.

Deferred Delivery Cancellation
      N/A (local).

Delivery Notification
      Supported.  This is performed at the gateway.  Thus, a
      notification is sent by the gateway to the originator.  If
      the 822-MTS protocol is JNT Mail, a notification may also be
      sent by the recipient UA.

Delivery via Bureaufax Service
      N/A (PDAU).

Designation of Recipient by Directory Name
      N/A (local).

Disclosure of Other Recipients
      Supported by use of a new RFC 822 header (X400-Recipients:).
      This is descriptive information for the RFC 822 recipient,
      and is not reverse mappable.

DL Expansion History Indication
      Supported by use of a new RFC 822 header
      DL-Expansion-History:).

DL Expansion Prohibited
      Distribution List means MTS supported distribution list, in
      the manner of X.400.  This service does not exist in the RFC
      822 world.  RFC 822 distribution lists should be regarded as
      an informal redistribution mechanism, beyond the scope of
      this control.  Messages will be sent to RFC 822,
      irrespective of whether this service is requested.
      Theoretically therefore, this service is supported, although
      in practice it may appear that it is not supported.

Express Mail Service
      N/A (PDAU).

Expiry Date Indication
      Supported as new RFC 822 header (Expiry-Date:).  In general,
      no automatic action can be expected.

Explicit Conversion
      N/A (prior).

Forwarded IP Message Indication
      Supported, with some loss of information.  The message is
      forwarded in an RFC 822 body, and so can only be interpreted
      visually.

Grade of Delivery Selection
      N/A (PDAU)

Importance Indication
      Supported as new RFC 822 header (Importance:).

Incomplete Copy Indication
      Supported as new RFC 822 header (Incomplete-Copy:).

Language Indication
      Supported as new RFC 822 header (Language:).

Latest Delivery Designation
      Not supported.  A new RFC 822 header (Latest-Delivery-Time:)
      is provided, which may be used by the recipient.

Message Flow Confidentiality
      Not supported.

Message Origin Authentication
      N/A (reception).

Message Security Labelling
      Not supported.

Message Sequence Integrity
      Not supported.

Multi-Destination Delivery
      Supported.

Multi-part Body
      Supported, with some loss of information, in that the
      structuring cannot be formalised in RFC 822.

Non Receipt Notification Request
      Not supported.

Non Repudiation of Delivery
      Not supported.

Non Repudiation of Origin
      N/A (reception).

Non Repudiation of Submission
      N/A (local).

Obsoleting Indication
      Supported as new RFC 822 header (Obsoletes:).

Ordinary Mail
      N/A (PDAU).

Originator Indication
      Supported.

Originator Requested Alternate Recipient
      Not supported, but is placed as comment next to address
      X400-Recipients:).

Physical Delivery Notification by MHS
      N/A (PDAU).

Physical Delivery Notification by PDS
      N/A (PDAU).

Physical Forwarding Allowed
      Supported by use of a comment in a new RFC 822 header
      X400-Recipients:), associated with the recipient in
      question.

Physical Forwarding Prohibited
      Supported by use of a comment in a new RFC 822 header
      X400-Recipients:), associated with the recipient in
      question.

Prevention of Non-delivery notification
      Supported, as delivery notifications cannot be generated by
      RFC 822.  In practice, errors will be returned as IP
      Messages, and so this service may appear not to be supported
      see Non-delivery Notification).

Primary and Copy Recipients Indication
      Supported

Probe
      Supported at the gateway (i.e., the gateway services the
      probe).

Probe Origin Authentication
      N/A (reception).

Proof of Delivery
      Not supported.

Proof of Submission
      N/A (local).

Receipt Notification Request Indication
      Not supported.

Redirection Allowed by Originator
      Redirection means MTS supported redirection, in the manner
      of X.400.  This service does not exist in the RFC 822 world.
      RFC 822 redirection (e.g., aliasing) should be regarded as
      an informal redirection mechanism, beyond the scope of this
      control.  Messages will be sent to RFC 822, irrespective of
      whether this service is requested.  Theoretically therefore,
      this service is supported, although in practice it may
      appear that it is not supported.

Registered Mail
      N/A (PDAU).

Registered Mail to Addressee in Person
      N/A (PDAU).

Reply Request Indication
      Supported as comment next to address.

Replying IP Message Indication
      Supported.

Report Origin Authentication
      N/A (reception).

Request for Forwarding Address
      N/A (PDAU).

Requested Delivery Method
      N/A (local).   The services required must be dealt with at
      submission time.  Any such request is made available through
      the gateway by use of a comment associated with the
      recipient in question.

Return of Content
      In principle, this is N/A, as non-delivery notifications are
      not supported.  In practice, most RFC 822 systems will
      return part or all of the content along with the IP Message
      indicating an error (see Non-delivery Notification).

Sensitivity Indication
      Supported as new RFC 822 header (Sensitivity:).

Special Delivery
      N/A (PDAU).

Stored Message Deletion
      N/A (MS).

Stored Message Fetching
      N/A (MS).

Stored Message Listing
      N/A (MS).

Stored Message Summary
      N/A (MS).

Subject Indication
      Supported.

Undeliverable Mail with Return of Physical Message
      N/A (PDAU).

Use of Distribution List
      In principle this applies only to X.400 supported
      distribution lists (see DL Expansion Prohibited).
      Theoretically, this service is N/A (prior).  In practice,
      because of informal RFC 822 lists, this service can be
      regarded as supported.

2.3.2.  Reception by X.400

2.3.2.1.  Standard Mandatory Services

   The following standard IPM mandatory  user facilities are required
   for reception of RFC 822 originated mail by an X.400 UA.

   Content Type Indication

   Delivery Time Stamp Indication

   IP Message Identification

   Message Identification

   Non-delivery Notification

   Original Encoded Information Types Indication

   Submission Time Stamp Indication

   Typed Body

2.3.2.2.  Standard Optional Services

   The following standard IPM optional user facilities are required for
   reception of RFC 822 originated mail by an X.400 UA.

   Authorising User's Indication

   Blind Copy Recipient Indication

   Cross Referencing Indication

   Originator Indication

   Primary and Copy Recipients Indication

   Replying IP Message Indication

   Subject Indication

2.3.2.3.  New Services

   A new service "RFC 822 Header Field" is defined using the extension
   facilities.  This allows for any RFC 822 header field to be
   represented.  It may be present in RFC 822 originated messages, which
   are received by an X.400 UA.

Chapter 3 Basic Mappings

3.1.  Notation

   The X.400 protocols are encoded in a structured manner according to
   ASN.1, whereas RFC 822 is text encoded.  To define a detailed
   mapping, it is necessary to refer to detailed protocol elements in
   each format.  A notation to achieve this is described in this
   section.

3.1.1.  RFC 822

   Structured text is defined according to the Extended Backus Naur Form
   (EBNF) defined in Section 2 of RFC 822 [Crocker82a].  In the EBNF
   definitions used in this specification, the syntax rules given in
   Appendix D of RFC 822 are assumed.  When these EBNF tokens are
   referred to outside an EBNF definition, they are identified by the
   string "822." appended to the beginning of the string (e.g.,
   822.addr-spec).  Additional syntax rules, to be used throughout this
   specification, are defined in this chapter.

   The EBNF is used in two ways.

   1.   To describe components of RFC 822 messages (or of 822-MTS
        components).  In this case, the lexical analysis defined in
        Section 3 of RFC 822 shall be used.  When these new EBNF
        tokens are referred to outside an EBNF definition, they are
        identified by the string "EBNF." appended to the beginning
        of the string (e.g., EBNF.importance).

   2.   To describe the structure of IA5 or ASCII information not in
        an RFC 822 message.  In these cases, tokens will either be
        self delimiting, or be delimited by self delimiting tokens.
        Comments and LWSP are not used as delimiters, except for the
        following cases, where LWSP may be inserted according to RFC
        822 rules.

   -         Around the ":" in all headers

   -         EBNF.labelled-integer

   -         EBNF.object-identifier

   -         EBNF.encoded-info

   RFC 822 folding rules are applied to all headers.

3.1.2.  ASN.1

   An element is referred to with the following syntax, defined in EBNF:

        element         = service "." definition *( "." definition )
        service         = "IPMS" / "MTS" / "MTA"
        definition      = identifier / context
        identifier      = ALPHA *< ALPHA or DIGIT or "-" >
        context         = "[" 1*DIGIT "]"

   The EBNF.service keys are shorthand for the following service
   specifications:

      IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
           10021-7.

      MTS  MTSAbstractService defined in Section 9 of X.411 / ISO
           10021-4.

      MTA  MTAAbstractService defined in Section 13 of X.411 / ISO
           10021-4.

   The first EBNF.identifier identifies a type or value key in the
   context of the defined service specification.   Subsequent
   EBNF.identifiers identify a value label or type in the context of the
   first identifier (SET or SEQUENCE).  EBNF.context indicates a context
   tag, and is used where there is no label or type to uniquely identify
   a component.  The special EBNF.identifier keyword "value" is used to
   denote an element of a sequence.

   For example, IPMS.Heading.subject defines the subject element of the
   IPMS heading.  The same syntax is also used to refer to element
   values.  For example,

   MTS.EncodedInformationTypes.[0].g3Fax refers to a value of
   MTS.EncodedInformationTypes.[0] .

3.2.  ASCII and IA5

   A gateway will interpret all IA5 as ASCII.  Thus, mapping between
   these forms is conceptual.

3.3.  Standard Types

   There is a need to convert between ASCII text, and some of the types
   defined in ASN.1 [CCITT/ISO88d].  For each case, an EBNF syntax
   definition is given, for use in all of this specification, which
   leads to a mapping between ASN.1, and an EBNF construct.  All EBNF
   syntax definitions of ASN.1 types are in lower case, whereas ASN.1
   types are referred to with the first letter in upper case.  Except as
   noted, all mappings are symmetrical.

3.3.1.  Boolean

   Boolean is encoded as:

           boolean = "TRUE" / "FALSE"

3.3.2.  NumericString

   NumericString is encoded as:

           numericstring = *DIGIT

3.3.3.  PrintableString

   PrintableString is a restricted IA5String defined as:

           printablestring  = *( ps-char )
           ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                              / "," / "-" / "." / "/" / ":" / "=" / "?"
           ps-delim         = "(" / ")"
           ps-char          = ps-delim / ps-restricted-char

   This can be used to represent real printable strings in EBNF.

3.3.4.  T.61String

   In cases where T.61 strings are only used for conveying human
   interpreted information, the aim of a mapping is  to render the
   characters appropriately in the remote character set, rather than to
   maximise reversibility.  For these cases, the mappings to IA5 defined
   in CCITT Recommendation X.408 (1988) shall be used [CCITT/ISO88a].
   These will then be encoded in ASCII.

   There is also a need to represent Teletex Strings in ASCII, for some
   aspects of O/R Address.  For these, the following encoding is used:

           teletex-string   = *( ps-char / t61-encoded )
           t61-encoded      = "{" 1* t61-encoded-char "}"
           t61-encoded-char = 3DIGIT

   Common characters are mapped simply.  Other octets are mapped using a
   quoting mechanism similar to the printable string mechanism.  Each
   octet is represented as 3 decimal digits.

   There are a number of places where a string may have a Teletex and/or
   Printable String representation.  The following BNF is used to
   represent this.

      teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]

   The natural mapping is restricted to EBNF.ps-char, in order to make
   the full BNF easier to parse.

3.3.5.  UTCTime

   Both UTCTime and the RFC 822 822.date-time syntax contain:  Year
   (lowest two digits), Month, Day of Month, hour, minute, second
   (optional), and Timezone.  822.date-time also contains an optional
   day of the week, but this is redundant.  Therefore a symmetrical
   mapping can be made between these constructs.

   Note:
        In practice, a gateway will need to parse various illegal
        variants on 822.date-time.  In cases where 822.date-time
        cannot be parsed, it is recommended that the derived UTCTime
        is set to the value at the time of translation.

   When mapping to X.400, the UTCTime format which specifies the
   timezone offset shall be used.

   When mapping to RFC 822, the 822.date-time format shall include a
   numeric timezone offset (e.g., +0000).

   When mapping time values, the timezone shall be preserved as
   specified.  The date shall not be normalised to any other timezone.

3.3.6.  Integer

   A basic ASN.1 Integer will be mapped onto EBNF.numericstring.  In
   many cases ASN.1 will enumerate Integer values or use ENUMERATED.  An
   EBNF encoding labelled-integer is provided. When mapping from EBNF to

   ASN.1, only the integer value is mapped, and the associated text is
   discarded.  When mapping from ASN.1 to EBNF, addition of an
   appropriate text label is strongly encouraged.

        labelled-integer ::= [ key-string ] "(" numericstring ")"

        key-string      = *key-char
        key-char        = <a-z, A-Z, 0-9, and "-">

3.3.7.  Object Identifier

   Object identifiers are represented in a form similar to that given in
   ASN.1.  The order is the same as for ASN.1 (big-endian).  The numbers
   are mandatory, and used when mapping from the ASCII to ASN.1.  The
   key-strings are optional.  It is recommended that as many strings as
   possible are generated when mapping from ASN.1 to ASCII, to
   facilitate user recognition.

        object-identifier  ::= oid-comp object-identifier
                        | oid-comp

        oid-comp ::= [ key-string ] "(" numericstring ")"

An example representation of an object identifier is:

        joint-iso-ccitt(2) mhs (6) ipms (1) ep (11) ia5-text (0)

        or

        (2) (6) (1)(11)(0)

3.4.  Encoding ASCII in Printable String

   Some information in RFC 822 is represented in ASCII, and needs to be
   mapped into X.400 elements encoded as printable string.  For this
   reason, a mechanism to represent ASCII encoded as PrintableString is
   needed.

   A structured subset of EBNF.printablestring is now defined.  This
   shall be used to encode ASCII in the PrintableString character set.

        ps-encoded       = *( ps-restricted-char / ps-encoded-char )
        ps-encoded-char  = "(a)"               ; (@)
                         / "(p)"               ; (%)
                         / "(b)"               ; (!)
                         / "(q)"               ; (")
                         / "(u)"               ; (_)
                         / "(l)"               ; "("
                         / "(r)"               ; ")"
                         / "(" 3DIGIT ")"

   The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and is
   interpreted in decimal as the corresponding ASCII character.  Special
   encodings are given for: at sign (@), percent (%), exclamation
   mark/bang (!), double quote ("), underscore (_), left bracket ((),
   and right bracket ()).  These characters, with the exception of round
   brackets, are not included in PrintableString, but are common in RFC
   822 addresses.  The abbreviations will ease specification of RFC 822
   addresses from an X.400 system.  These special encodings shall be
   interpreted in a case insensitive manner, but always generated in
   lower case.

   A reversible mapping between PrintableString and ASCII can now be
   defined.  The reversibility means that some values of printable
   string (containing round braces) cannot be generated from ASCII.
   Therefore, this mapping must only be used in cases where the
   printable strings may only be derived from ASCII (and will therefore
   have a restricted domain).  For example, in this specification, it is
   only applied to a Domain Defined Attribute which will have been
   generated by use of this specification and a value such as "(" would
   not be possible.

   To encode ASCII as PrintableString, the EBNF.ps-encoded syntax is
   used, with all EBNF.ps-restricted-char mapped directly.  All other
   822.CHAR are encoded as EBNF.ps-encoded-char.

   To encode PrintableString as ASCII, parse PrintableString as
   EBNF.ps-encoded, and then reverse the previous mapping.  If the
   PrintableString cannot be parsed, then the mapping is being applied
   in to an inappropriate value, and an error shall be given to the
   procedure doing the mapping. In some cases, it may be preferable to
   pass the printable string through unaltered.

   Some examples are now given.  Note the arrows which indicate
   asymmetrical mappings:

                PrintableString           ASCII

                'a demo.'         <->   'a demo.'
                foo(a)bar         <->   foo@bar
                (q)(u)(p)(q)      <->   "_%"
                (a)               <->   @
                (A)               ->    @
                (l)a(r)           <->   (a)
                (126)             <->   ~
                (                 ->    (
                (l)               <->   (

Chapter 4 - Addressing

   Addressing is probably the trickiest problem of an X.400 <-> RFC 822
   gateway.  Therefore it is given a separate chapter.  This chapter, as
   a side effect, also defines a textual representation of an X.400 O/R
   Address.

   Initially we consider an address in the (human) mail user sense of
   "what is typed at the mailsystem to reference a mail user".  A basic
   RFC 822 address is defined by the EBNF EBNF.822-address:

           822-address     = [ route ] addr-spec

   In an 822-MTS protocol, the originator and each recipient are
   considered to be defined by such a construct.  In an RFC 822 header,
   the EBNF.822-address is encapsulated in the 822.address syntax rule,
   and there may also be associated comments.  None of this extra
   information has any semantics, other than to the end user.

   The basic X.400 O/R Address, used by the MTS for routing, is defined
   by MTS.ORAddress.  In IPMS, the MTS.ORAddress is encapsulated within
   IPMS.ORDescriptor.

   It can be seen that RFC 822 822.address must be mapped with
   IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
   with MTS.ORAddress.

4.1.  A textual representation of MTS.ORAddress

   MTS.ORAddress is structured as a set of attribute value pairs.  It is
   clearly necessary to be able to encode this in ASCII for gatewaying
   purposes.  All components shall be encoded, in order to guarantee
   return of error messages, and to optimise third party replies.

4.2.  Basic Representation

   An O/R Address has a number of structured and unstructured
   attributes.  For each unstructured attribute, a key and an encoding
   is specified.  For structured attributes, the X.400 attribute is
   mapped onto one or more attribute value pairs.  For domain defined
   attributes, each element of the sequence will be mapped onto a triple
   (key and two values), with each value having the same encoding.  The
   attributes are as follows, with 1984 attributes given in the first
   part of the table.  For each attribute, a reference is given,
   consisting of the relevant sections in X.402 / ISO 10021-2, and the
   extension identifier for 88 only attributes:

  Attribute (Component)                Key          Enc     Ref     Id

84/88 Attributes

MTS.CountryName                        C              P     18.3.3
MTS.AdministrationDomainName           ADMD           P     18.3.1
MTS.PrivateDomainName                  PRMD           P     18.3.21
MTS.NetworkAddress                     X121           N     18.3.7
MTS.TerminalIdentifier                 T-ID           P     18.3.23
MTS.OrganizationName                   O              P/T   18.3.9
MTS.OrganizationalUnitNames.value      OU             P/T   18.3.10
MTS.NumericUserIdentifier              UA-ID          N     18.3.8
MTS.PersonalName                       PN             P/T   18.3.12
MTS.PersonalName.surname               S              P/T   18.3.12
MTS.PersonalName.given-name            G              P/T   18.3.12
MTS.PersonalName.initials              I              P/T   18.3.12
MTS.PersonalName
   .generation-qualifier               GQ             P/T   18.3.12
MTS.DomainDefinedAttribute.value       DD             P/T   18.1

88 Attributes

MTS.CommonName                         CN             P/T   18.3.2    1
MTS.TeletexCommonName                  CN             P/T   18.3.2    2
MTS.TeletexOrganizationName            O              P/T   18.3.9    3
MTS.TeletexPersonalName                PN             P/T   18.3.12   4
MTS.TeletexPersonalName.surname        S              P/T   18.3.12   4
MTS.TeletexPersonalName.given-name     G              P/T   18.3.12   4
MTS.TeletexPersonalName.initials       I              P/T   18.3.12   4
MTS.TeletexPersonalName
    .generation-qualifier              GQ             P/T   18.3.12   4
MTS.TeletexOrganizationalUnitNames
   .value                              OU             P/T   18.3.10   5
MTS.TeletexDomainDefinedAttribute
   .value                              DD             P/T   18.1      6

MTS.PDSName                            PD-SERVICE     P     18.3.11   7
MTS.PhysicalDeliveryCountryName        PD-C           P     18.3.13   8
MTS.PostalCode                         PD-CODE        P     18.3.19   9
MTS.PhysicalDeliveryOfficeName         PD-OFFICE      P/T   18.3.14   10
MTS.PhysicalDeliveryOfficeNumber       PD-OFFICE-NUM  P/T   18.3.15   11
MTS.ExtensionORAddressComponents       PD-EXT-ADDRESS P/T   18.3.4    12
MTS.PhysicalDeliveryPersonName         PD-PN          P/T   18.3.17   13
MTS.PhysicalDeliveryOrganizationName   PD-O           P/T   18.3.16   14
MTS.ExtensionPhysicalDelivery
   AddressComponents                  PD-EXT-DELIVERY P/T   18.3.5    15
MTS.UnformattedPostalAddress           PD-ADDRESS     P/T   18.3.25   16
MTS.StreetAddress                      PD-STREET      P/T   18.3.22   17
MTS.PostOfficeBoxAddress               PD-BOX         P/T   18.3.18   18
MTS.PosteRestanteAddress               PD-RESTANTE    P/T   18.3.20   19
MTS.UniquePostalName                   PD-UNIQUE      P/T   18.3.26   20
MTS.LocalPostalAttributes              PD-LOCAL       P/T   18.3.6    21
MTS.ExtendedNetworkAddress
   .e163-4-address.number              NET-NUM        N     18.3.7    22
MTS.ExtendedNetworkAddress
   .e163-4-address.sub-address         NET-SUB        N     18.3.7    22
MTS.ExtendedNetworkAddress
   .psap-address                       NET-PSAP       X     18.3.7    22
MTS.TerminalType                       T-TY           I     18.3.24   23

   The following keys identify different EBNF encodings, which are
   associated with the ASCII representation of MTS.ORAddress.

                   Key         Encoding

                   P     printablestring
                   N     numericstring
                   T     teletex-string
                   P/T   teletex-and-or-ps
                   I     labelled-integer
                   X     presentation-address

   The BNF for presentation-address is taken from the specification "A
   String Encoding of Presentation Address" [Kille89a].

   In most cases, the EBNF encoding maps directly to the ASN.1 encoding
   of the attribute.  There are a few exceptions. In cases where an
   attribute can be encoded as either a PrintableString or NumericString
   (Country, ADMD, PRMD), either form is mapped into the BNF.  When
   generating ASN.1, the NumericString encoding shall be used if the
   string contains only digits.

   There are a number of cases where the P/T (teletex-and-or-ps)
   representation is used.  Where the key maps to a single attribute,

   this choice is reflected in the encoding of the attribute (attributes
   10-21).  For most of the 1984 attributes and common name, there is a
   printablestring and a teletex variant.   This pair of attributes is
   mapped onto the single component here.  This will give a clean
   mapping for the common cases where only one form of the name is used.

   Recently, ISO has undertaken work to specify a string form of O/R
   Address [CCITT/ISO91a].  This has specified a number of string
   keywords for attributes.  As RFC 1148 was an input to this work, many
   of the keywords are the same.  To increase compatability, the
   following alternative values shall be recognised when mapping from
   RFC 822 to X.400.  These shall not be generated when mapping from
   X.400 to RFC 822.

                   Keyword          Alternative

               ADMD               A
               PRMD               P
               GQ                 Q
               X121               X.121
               UA-ID              N-ID
               PD-OFFICE-NUMBER   PD-OFFICE NUMBER

   When mapping from RFC 822 to X.400, the keywords: OU1, OU2, OU3, and
   OU4, shall be recognised.    If these are present, no keyword OU
   shall be present.  These will be treated as ordered values of OU.

4.2.1.  Encoding of Personal Name

   Handling of Personal Name and Teletex Personal Name based purely on
   the EBNF.standard-type syntax defined above is likely to be clumsy.
   It seems desirable to utilise the "human" conventions for encoding
   these components.  A syntax is defined, which is designed to provide
   a clean encoding for the common cases of O/R Address specification
   where:

   1.   There is no generational qualifier

   2.   Initials contain only letters

   3.   Given Name does not contain full stop ("."), and is at least
        two characters long.

   4.   Surname does not contain full stop in the first two
        characters.

   5    If Surname is the only component, it does not contain full
        stop.

   The following EBNF is defined:

           encoded-pn      = [ given "." ] *( initial "." ) surname

           given           = 2*<ps-char not including ".">

           initial         = ALPHA

           surname         = printablestring

   This is used to map from any string containing only printable string
   characters to an O/R address personal name.  To map from a string to
   O/R Address components, parse the string according to the EBNF.  The
   given name and surname are assigned directly.  All EBNF.initial
   tokens are concatenated without intervening full stops to generate
   the initials component.

   For an O/R address which follows the above restrictions, a string is
   derived in the natural manner.  In this case, the mapping will be
   reversible.

   For example:

        GivenName       = "Marshall"
        Surname         = "Rose"

        Maps with  "Marshall.Rose"

        Initials        = "MT"
        Surname         = "Rose"

        Maps with  "M.T.Rose"

        GivenName       = "Marshall"
        Initials        = "MT"
        Surname         = "Rose"

        Maps with  "Marshall.M.T.Rose"

   Note that X.400 suggest that Initials is used to encode ALL initials.
   Therefore, the defined encoding is "natural" when either GivenName or
   Initials, but not both, are present.  The case where both are present
   can be encoded, but this appears to be contrived!

4.2.2.  Standard Encoding of MTS.ORAddress

   Given this structure, we can specify a BNF representation of an O/R
   Address.

        std-or-address  = 1*( "/" attribute "=" value ) "/"
        attribute       = standard-type
                        / "RFC-822"
                        / registered-dd-type
                        / dd-key "." std-printablestring
        standard-type   = key-string

        registered-dd-type
                        = key-string
        dd-key          = key-string

        value           = std-printablestring

        std-printablestring
                        = *( std-char / std-pair )
        std-char        = <"{", "}", "*", and any ps-char
                                        except "/" and "=">
        std-pair        = "$" ps-char

   The standard-type is any key defined in the table in Section 4.2,
   except PN, and DD.  The BNF leads to a set of attribute/value pairs.
   The value is interpreted according to the EBNF encoding defined in
   the table.

   If the standard-type is PN, the value is interpreted according to
   EBNF.encoded-pn, and the components of MTS.PersonalName and/or
   MTS.TeletexPersonalName derived accordingly.

   If dd-key is the recognised Domain Defined string (DD), then the type
   and value are interpreted according to the syntax implied from the
   encoding, and aligned to either the teletex or printable string form.
   Key and value shall have the same encoding.

   If value is "RFC-822", then the (printable string) Domain Defined
   Type of "RFC-822" is assumed.  This is an optimised encoding of the
   domain defined type defined by this specification.

   The matching of all keywords shall be done in a case-independent
   manner.

   EBNF.std-or-address uses the characters "/" and "=" as delimiters.
   Domain Defined Attributes and any value may contain these characters.
   A quoting mechanism, using the non-printable string "$" is used to
   allow these characters to be represented.

   If the value is registered-dd-type, and the value is registered at
   the Internet Assigned Numbers Authority (IANA) as an accepted Domain
   Defined Attribute type, then the value shall be interpreted

   accordingly.  This restriction maximises the syntax checking which
   can be done at a gateway.

4.3.  EBNF.822-address <-> MTS.ORAddress

   Ideally, the mapping specified would be entirely symmetrical and
   global, to enable addresses to be referred to transparently in the
   remote system, with the choice of gateway being left to the Message
   Transfer Service.  There are two fundamental reasons why this is not
   possible:

   1.   The syntaxes are sufficiently different to make this
        awkward.

   2.   In the general case, there would not be the necessary
        administrative co-operation between the X.400 and RFC 822
        worlds, which would be needed for this to work.

   Therefore, an asymmetrical mapping is defined, which can be
   symmetrical where there is appropriate administrative control.

4.3.1.  X.400 encoded in RFC 822

   The std-or-address syntax is  used to encode O/R Address information
   in the 822.local-part of EBNF.822-address.  In some cases, further
   O/R Address information is associated with the 822.domain component.
   This cannot be used in the general case, due to character set
   problems, and to the variants of X.400 O/R Addresses which use
   different attribute types.  The only way to encode the full
   PrintableString character set in a domain is by use of the
   822.domain-ref syntax (i.e. 822.atom).  This is likely to cause
   problems on many systems.  The effective character set of domains is
   in practice reduced from the RFC 822 set, by restrictions imposed by
   domain conventions and policy, and by restrictions in RFC 821.

   A generic 822.address consists of a 822.local-part and a sequence of
   822.domains (e.g., <@domain1,@domain2:user@domain3>).  All except the
   822.domain associated with the 822.local-part (domain3 in this case)
   are considered to specify routing within the RFC 822 world, and will
   not be interpreted by the gateway (although they may have identified
   the gateway from within the RFC 822 world).

   The  822.domain associated with the 822.local-part identifies the
   gateway from within the RFC 822 world.  This final 822.domain may be
   used to determine some number of O/R Address attributes, where this
   does not conflict with the first role.  RFC 822 routing to gateways
   will usually be set up to facilitate the 822.domain being used for
   both purposes.  The following O/R Address attributes are considered

   as a hierarchy, and may be specified by the domain.  They are (in
   order of hierarchy):

        Country, ADMD, PRMD, Organisation, Organisational Unit

   There may be multiple Organisational Units.

   A global mapping is defined between domain specifications, and some
   set of attributes.  This association proceeds hierarchically.  For
   example, if a domain implies ADMD, it also implies country.
   Subdomains under this are associated according to the O/R Address
   hierarchy.  For example:

        => "AC.UK" might be associated with
        C="GB", ADMD="GOLD 400", PRMD="UK.AC"

        then domain "R-D.Salford.AC.UK" maps with
        C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"

   There are three basic reasons why a domain/attribute mapping might be
   maintained, as opposed to using simply subdomains:

   1.   As a shorthand to avoid redundant X.400 information.  In
        particular, there will often be only one ADMD per country,
        and so it does not need to be given explicitly.

   2.   To deal with cases where attribute values do not fit the
        syntax:

           domain-syntax   = alphanum [ *alphanumhyphen alphanum ]
           alphanum        = <ALPHA or DIGIT>
           alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>

        Although RFC 822 allows for a more general syntax, this
        restricted syntax is chosen as it is the one chosen by the
        various domain service administrations.

   3.   To deal with missing elements in the hierarchy.  A domain
        may be associated with an omitted attribute in conjunction
        with several present ones.  When performing the algorithmic
        insertion of components lower in the hierarchy, the omitted
        value shall be skipped.  For example, if "HNE.EGM" is
        associated with "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted
        organisation, then "ZI.HNE.EGM" is mapped with "C=TC",
        "ADMD=ECQ", "PRMD=HNE", "OU=ZI". Attributes may have null
        values, and  this is treated separately from omitted
        attributes (whilst it would be bad practice to treat these

        two cases differently, they must be allowed for).

   This set of mappings needs  be known by the gateways relaying between
   the RFC 822 world, and the O/R Address space associated with the
   mapping in question.  There needs to be a single global definition of
   this set of mappings.  A mapping implies an adminstrative equivalence
   between the two parts of the namespaces which are mapped together.
   To correctly route in all cases, it is necessary for all gateways to
   know the mapping.  To facilitate distribution of a global set of
   mappings, a format for the exchange of this information is defined in
   Appendix F.

   The remaining attributes are encoded on the LHS, using the EBNF.std-
   or-address syntax.  For example:

        /I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM

   encodes the MTS.ORAddress consisting of:

        MTS.CountryName                       = "TC"
        MTS.AdministrationDomainName          = "BTT"
        MTS.OrganizationName                  = "Widget"
        MTS.OrganizationalUnitNames.value     = "Marketing"
        MTS.PersonalName.surname              = "Linnimouth"
        MTS.PersonalName.initials             = "J"
        MTS.PersonalName.generation-qualifier = "5"

   The first three attributes are determined by the domain Widget.COM.
   Then, the first element of OrganizationalUnitNames is determined
   systematically, and the remaining attributes are encoded on the LHS.
   In an extreme case, all of the attributes will be on the LHS.  As the
   domain cannot be null, the RHS will simply be a domain indicating the
   gateway.

   The RHS (domain) encoding is designed to deal cleanly with common
   addresses, and so the amount of information on the RHS is maximised.
   In particular, it covers the Mnemonic O/R Address using a 1984
   compatible encoding.  This is seen as the dominant form of O/R
   Address.  Use of other forms of O/R Address, and teletex encoded
   attributes will require an LHS encoding.

   There is a further mechanism to simplify the encoding of common
   cases, where the only attributes to be encoded on the LHS is a (non-
   Teletex) Personal Name attributes which comply with the restrictions
   of 4.2.1.  To achieve this, the 822.local-part shall be encoded as
   EBNF.encoded-pn.  In the previous example, if the GenerationQualifier
   was not present in the previous example O/R Address, it would map
   with the RFC 822 address: J.Linnimouth@Marketing.Widget.COM.

   From the standpoint of the RFC 822 Message Transfer System, the
   domain specification is simply used to route the message in the
   standard manner.  The standard domain mechanisms are used to select
   appropriate gateways for the corresponding O/R Address space.  In
   most cases, this will be done by registering the higher levels, and
   assuming that the gateway can handle the lower levels.

4.3.2.  RFC 822 encoded in X.400

   In some cases, the encoding defined above may be reversed, to give a
   "natural" encoding of genuine RFC 822 addresses.  This depends
   largely on the allocation of appropriate management domains.

   The general case is mapped by use of domain defined attributes.  A
   Domain defined type "RFC-822" is defined. The associated attribute
   value is an ASCII string encoded according to Section 3.3.3 of this
   specification. The interpretation of the ASCII string depends on the
   context of the gateway.

   1.   In the context of RFC 822, and RFC 920
        [Crocker82a,Postel84a], the string can be used directly.

   2.   In the context of the JNT Mail protocol, and the NRS
        [Kille84a,Larmouth83a], the string shall be interpreted
        according to Mailgroup Note 15 [Kille84b].

   3.   In the context of UUCP based systems, the string shall be
        interpreted as defined in [Horton86a].

   Other O/R Address attributes will be used to identify a context in
   which the O/R Address will be interpreted.  This might be a
   Management Domain, or some part of a Management Domain which
   identifies a gateway MTA.  For example:

           C               = "GB"
           ADMD            = "GOLD 400"
           PRMD            = "UK.AC"
           O               = "UCL"
           OU              = "CS"
           "RFC-822"      =  "Jimmy(a)WIDGET-LABS.CO.UK"

   OR

           C               = "TC"
           ADMD            = "Wizz.mail"
           PRMD            = "42"
           "rfc-822"       = "postel(a)venera.isi.edu"

   Note in each case the PrintableString encoding of "@" as "(a)".  In
   the second example, the "RFC-822" domain defined attribute is
   interpreted everywhere within the (Private) Management Domain.  In
   the first example, further attributes are needed within the
   Management Domain to identify a gateway.  Thus, this scheme can be
   used with varying levels of Management Domain co-operation.

   There is a limit of 128 characters in the length of value of a domain
   defined attribute, and an O/R Address can have a maxmimum of four
   domain defined attributes.  Where the printable string generated from
   the RFC 822 address exceeeds this value, additional domain defined
   attributes are used to enable up to 512 characters to be encoded.
   These attributes shall be filled completely before the next one is
   started.   The DDA keywords are:  RFC822C1; RFC822C2; RFC822C3.
   Longer addresses cannot be encoded.

   There is, analagous with 4.3.1, a means to associate parts of the O/R
   Address hierarchy with domains.  There is an analogous global
   mapping, which in most cases will be the inverse of the domain to O/R
   address mapping.  The mapping is maintained separately, as there may
   be differences (e.g., two alternate domain names map to the same set
   of O/R address components).

4.3.3.  Component Ordering

   In most cases, ordering of O/R Address components is not significant
   for the mappings specified.  However, Organisational Units (printable
   string and teletex forms) and Domain Defined Attributes are specified
   as SEQUENCE in MTS.ORAddress, and so their order may be significant.
   This specification needs to take account of this:

   1.   To allow consistent mapping into the domain hierarchy

   2.   To ensure preservation of order over multiple mappings.

   There are three places where an order is specified:

   1.   The text encoding (std-or-address) of MTS.ORAddress as used
        in the local-part of an RFC 822 address.  An order is needed
        for those components which may have multiple values
        (Organisational Unit, and Domain Defined Attributes). When
        generating an 822.std-or-address, components of a given type
        shall be in hierarchical order with the most significant
        component on the RHS.  If there is an Organisation
        Attribute, it shall be to the right of any Organisational
        Unit attributes.  These requirements are for the following
        reasons:

   -         Alignment to the hierarchy of other components in RFC
             822 addresses (thus, Organisational Units will appear
             in the same order, whether encoded on the RHS or LHS).
             Note the differences of JNT Mail as described in
             Appendix B.

   -         Backwards compatibility with RFC 987/1026.

   -         To ensure that gateways generate consistent addresses.
             This is both to help end users, and to generate
             identical message ids.

        Further, it is recommended that all other attributes are
        generated according to this ordering, so that all attributes
        so encoded follow a consistent hierarchy.   When generating
        822.msg-id, this order shall be followed.

   2.   For the Organisational Units (OU) in MTS.ORAddress, the
        first OU in the SEQUENCE is the most significant, as
        specified in X.400.

   3.   For the Domain Defined Attributes in MTS.ORAddress, the
        First Domain Defined Attribute in the SEQUENCE is the most
        significant.

        Note that although this ordering is mandatory for this
        mapping, there are NO implications on ordering significance
        within X.400, where this is a Management Domain issue.

4.3.4.  RFC 822 -> X.400

   There are two basic cases:

   1.   X.400 addresses encoded in RFC 822.  This will also include
        RFC 822 addresses which are given reversible encodings.

   2.   "Genuine" RFC 822 addresses.

   The mapping shall proceed as follows, by first assuming case 1).

STAGE I.

   1.   If the 822-address is not of the form:

                local-part "@" domain

        take the domain which will be routed on and apply step 2 of
        stage 1 to derive (a possibly null) set of attributes. Then

        go to stage II.

        NOTE:It may be appropriate to reduce a source route address
             to this form by removal of all bar the last domain.  In
             terms of the design intentions of RFC 822, this would
             be an incorrect action.  However, in most real cases,
             it will do the "right" thing and provide a better
             service to the end user.  This is a reflection on the
             excessive and inappropriate use of source routing in
             RFC 822 based systems.  Either approach, or the
             intermediate approach of stripping only domain
             references which reference the local gateway are
             conformant to this specification.

   2.   Attempt to parse EBNF.domain as:

                *( domain-syntax "." ) known-domain

        Where EBNF.known-domain is the longest possible match in the
        set of globally defined mappings (see Appendix F).  If this
        fails, and the EBNF.domain does not explicitly identify the
        local gateway, go to stage II.  If the domain explicitly
        identifies the gateway, allocate no attributes.  Otherwise,
        allocate the attributes associated with EBNF.known-domain.
        For each component, systematically allocate the attribute
        implied by each EBNF.domain-syntax component in the order:
        C, ADMD, PRMD, O, OU.  Note that if the mapping used
        identifies an "omitted attribute", then this attribute
        should be omitted in the systematic allocation.  If this new
        component exceed an upper bound (ADMD: 16; PRMD: 16; O: 64;
        OU:  32) or it would lead to more than four OUs, then go to
        stage II with the attributes derived.

        At this stage, a set of attributes has been derived, which
        will give appropriate routing within X.400.  If any of the
        later steps of Stage I force use of Stage II, then these
        attributes should be used in Stage II.

   3.   If the 822.local-part uses the 822.quoted-string encoding,
        remove this quoting.  If this unquoted 822.local-part has
        leading space, trailing space, or two adjacent space go to
        stage II.

   4.   If the unquoted 822.local-part contains any characters not
        in PrintableString, go to stage II.

   5.   Parse the (unquoted) 822.local-part according to the EBNF
        EBNF.std-or-address.  Checking of upper bounds should not be

        done at this point.  If this parse fails, parse the local-
        part according to the EBNF EBNF.encoded-pn.  If this parse
        fails, go to stage II.  The result is a set of type/value
        pairs.  If the set of attributes leads to an address of any
        form other than mnemonic form, then only these attributes
        should be taken. If (for mnemonic form) the values generated
        conflict with those derived in step 2 (e.g., a duplicated
        country attribute), the domain is assumed to be a remote
        gateway.  In this case, take only the LHS derived
        attributes, together with any RHS dericed attributes which
        are more significant thant the most signicant attribute
        which is duplicated (e.g., if there is a duplicate PRMD, but
        no LHS derived ADMD and country, then the ADMD and country
        should be taken from the RHS).  therwise add LHS and RHS
        derived attributes together.

   6.   Associate the EBNF.attribute-value syntax (determined from
        the identified type) with each value, and check that it
        conforms.  If not, go to stage II.

   7.   Ensure that the set of attributes conforms both to the
        MTS.ORAddress specification and to the restrictions on this
        set given in X.400, and that no upper bounds are exceeded
        for any attribute.  If not go to stage II.

   8.   Build the O/R Address from this information.

STAGE II.

   This will only be reached if the RFC 822 EBNF.822-address is not a
   valid X.400 encoding.  This implies that the address must refer to a
   recipient on an RFC 822 system.  Such addresses shall be encoded in
   an X.400 O/R Address using a domain defined attribute.

   1.   Convert the EBNF.822-address to PrintableString, as
        specified in Chapter 3.

   2.   Generate the "RFC-822" domain defined attribute  from this
        string.

   3.   Build the rest of the O/R Address in the manner described
        below.

   It may not be possible to encode the domain defined attribute due to
   length restrictions.  If the limit is exceeded by a mapping at the
   MTS level, then the gateway shall reject the message in question.  If
   this occurs at the IPMS level, then the action will depend on the
   policy being taken for IPMS encoding, which is discussed in Section

   5.1.3.

   If Stage I has identified a set of attributes, use these to build the
   remainder of the address.  The administrative equivalence of the
   mappings will ensure correct routing throug X.400 to a gateway back
   to RFC 822.

   If Stage I has not identified a set of attributes, the remainder of
   the O/R address effectively identifies a source route to a gateway
   from the X.400 side.  There are three cases, which are handled
   differently:

   822-MTS Return Address
        This shall be set up so that errors are returned through the
        same gateway.  Therefore, the O/R Address of the local
        gateway shall be used.

   IPMS Addresses
        These are optimised for replying.  In general, the message
        may end up anywhere within the X.400 world, and so this
        optimisation identifies a gateway appropriate for  the RFC
        822 address being converted.  The 822.domain to which the
        address would be routed is used to select an appropriate
        gateway. A globally defined set of mappings is used, which
        identifies (the O/R Address components of) appropriate
        gateways for parts of the domain namespace.  The longest
        possible match on the 822.domain defines which gateway to
        use.  The table format for distribution of this information
        is defined in Appendix F.

        This global mapping is used for parts of the RFC 822
        namespace which do not have an administrative equivalence
        with any part of the X.400 namespace, but for which it is
        desirable to identify a preferred X.400 gateway in order to
        optimise routing.

        If no mapping is found for the 822.domain, a default value
        (typically that of the local gateway) is used.  It is never
        appropriate to ignore the globally defined mappings.  In
        some cases, it may be appropriate to locally override the
        globally defined mappings (e.g., to identify a gateway close
        to a recipient of the message).  This is likely to be where
        the global mapping identifies a public gateway, and the
        local gateway has an agreement with a private gateway which
        it prefers to use.

   822-MTS Recipient
        As the RFC 822 and X.400 worlds are fully connected, there

        is no technical reason for this situation to occur.  In some
        cases, routing may be configured to connect two parts of the
        RFC 822 world using X.400.  The information that this part
        of the domain space should be routed by X.400 rather than
        remaining within the RFC 822 world will be configured
        privately into the gateway in question.  The O/R address
        shall then be generated in the same manner as for an IPMS
        address, using the globally defined mappings. It is to
        support this case that the definition of the global domain
        to gateway mapping is important, as the use of this mapping
        will lead to a remote X.400 address, which can be routed by
        X.400 routing procedures.  The information in this mapping
        shall not be used as a basis for deciding to convert a
        message from RFC 822 to X.400.

4.3.4.1.  Heuristics for mapping RFC 822 to X.400

   RFC 822 users will often use an LHS encoded address to identify an
   X.400 recipient.  Because the syntax is fairly complex, a number of
   heuristics may be applied to facilitate this form of usage.  A
   gateway should take care not to be overly "clever" with heuristics,
   as this may cause more confusion than a more mechanical approach.
   The heuristics are as follows:

   1.   Ignore the omission of a trailing "/" in the std-or syntax.

   2.   If there is no ADMD component, and both country and PRMD are
        present, the value of /ADMD= / (single space) is assumed.

   3.   Parse the unquoted local part according to the EBNF colon-
        or-address.  This may facilitate users used to this
        delimiter.

        colon-or-address = 1*(attribute "=" value ";" *(LWSP-char))

   The remaining heuristic relates to ordering of address components.
   The ordering of attributes may be inverted or mixed.  For this
   reason, the following heuristics may be applied:

   4.   If there is an Organisation attribute to the left of any Org
        Unit attribute, assume that the hierarchy is inverted.

4.3.5.  X.400 -> RFC 822

   There are two basic cases:

   1.   RFC 822 addresses encoded in X.400.

   2.   "Genuine" X.400 addresses.  This may include symmetrically
        encoded RFC 822 addresses.

   When a MTS Recipient O/R Address is interpreted, gatewaying will be
   selected if there is a single "RFC-822" domain defined attribute
   present and the local gateway is identified by the remainder of the
   O/R Address.  In this case, use mapping A.  For other O/R Addresses
   which

   1.   Contain the special attribute.

        AND

   2.   Identifies the local gateway or any other known gateway with
        the other attributes.

   use mapping A.  In other cases, use mapping B.

   NOTE:
        A pragmatic approach would  be to assume that any O/R
        Address with the special domain defined attribute identifies
        an RFC 822 address. This will usually work correctly, but is
        in principle not correct.  Use of this approach is
        conformant to this specification.

Mapping A

   1.   Map the domain defined attribute value to ASCII, as defined
        in Chapter 3.

Mapping B

   This is used for X.400 addresses which do not use the explicit RFC
   822 encoding.

   1.   For all string encoded attributes, remove any leading or
        trailing spaces, and replace adjacent spaces with a single
        space.

        The only attribute which is permitted to have zero length is
        the ADMD.  This should be mapped onto a single space.

        These transformations are for lookup only.   If an
        EBNF.std-or-address mapping is used as in 4), then the
        orginal values should be used.

   2.   Map numeric country codes to the two letter values.

   3.   Noting the hierarchy specified in 4.3.1 and including
        omitted attributes, determine the maximum set of attributes
        which have an associated domain specification in the
        globally defined mapping.  If no match is found, allocate
        the domain as the domain specification of the local gateway,
        and go to step 5.

   Note:     It might be appropriate to use a non-local domain.
             This would be selected by a global mapping analagous to
             the one described at the end of 4.3.4.  This is not
             done, primarily because use of RFC 822 to connect X.400
             systems is not expected to be significant.

        In cases where the address refers to an X.400 UA, it is
        important that the generated domain will correctly route to
        a gateway.  In general, this is achieved by carefully co-
        ordinating RFC 822 routing with the definition of the global
        mappings, as there is no easy way for the gateway to make
        this check.  One rule that shall be used is that domains
        with only one component will not route to a gateway.  If the
        generated domain does not route correctly, the address is
        treated as if no match is found.

   4.   The mapping identified  in 3) gives a domain, and an O/R
        address prefix.  Follow the hierarchy: C, ADMD, PRMD, O, OU.
        For each successive component below the O/R address prefix,
        which conforms to the syntax EBNF.domain-syntax (as defined
        in 4.3.1), allocate the next subdomain.  At least one
        attribute of the X.400 address shall not be mapped onto
        subdomain, as 822.local-part cannot be null.  If there are
        omitted attributes in the O/R address prefix, these will
        have correctly and uniquely mapped to a domain component.
        Where there is an attribute omitted below the prefix, all
        attributes remaining in the O/R address shall be encoded on
        the LHS.  This is to ensure a reversible mapping. For
        example, if the is an addres /S=XX/O=YY/ADMD=A/C=NN/ and a
        mapping for /ADMD=A/C=NN/ is used, then /S=XX/O=YY/ is
        encoded on the LHS.

   5.   If the address is not  mnemonic form (form 1 variant 1),
        then all of the attributes in the address should be encoded
        on the LHS in EBNF.std-or-address syntax, as described
        below.

        For addresses of mnemonic form, if the remaining components
        are personal-name components, conforming to the restrictions
        of 4.2.1, then EBNF.encoded-pn is derived to form
        822.local-part.  In other cases the remaining components are

        simply encoded as 822.local-part using the
        EBNF.std-or-address syntax.  If necessary, the
        822.quoted-string encoding is used.  The following are
        examples of legal quoting: "a b".c@x; "a b.c"@x.  Either
        form may be generated, but the latter is preferred.

        If the derived 822.local-part can only be encoded by use of
        822.quoted-string, then use of the mapping defined
        in [Kille89b] may be appropriate.  Use of this mapping is
        discouraged.

4.4.  Repeated Mappings

   There are two types of repeated mapping:

   1.   A recursive mapping, where the repeat is within one gateway

   2    A source route, where the repetition occurs across multiple
        gateways

4.4.1.  Recursive Mappings

   It is possible to supply an address which is recurive at a single
   gateway.  For example:

           C          = "XX"
           ADMD       = "YY"
           O          = "ZZ"
           "RFC-822"  = "Smith(a)ZZ.YY.XX"

   This is mapped first to an RFC 822 address, and then back to the
   X.400 address:

           C          = "XX"
           ADMD       = "YY"
           O          = "ZZ"
           Surname    = "Smith"

   In some situations this type of recursion may be frequent.  It is
   important that where this occurs, that no unnecessary protocol
   conversion occurs. This will minimise loss of service.

4.4.2.  Source Routes

   The mappings defined are symmetrical and reversible across a single
   gateway.  The symmetry is particularly useful in cases of (mail
   exploder type) distribution list expansion.  For example, an X.400
   user sends to a list on an RFC 822 system which he belongs to.  The

   received message will have the originator and any 3rd party X.400 O/R
   Addresses in correct format (rather than doubly encoded).  In cases
   (X.400 or RFC 822) where there is common agreement on gateway
   identification, then this will apply to multiple gateways.

   When a message traverses multiple gateways, the mapping will always
   be reversible, in that a reply can be generated which will correctly
   reverse the path.  In many cases, the mapping will also be
   symmetrical, which will appear clean to the end user.  For example,
   if countries "AB" and "XY" have RFC 822 networks, but are
   interconnected by X.400, the following may happen:  The originator
   specifies:

           Joe.Soap@Widget.PTT.XY

   This is routed to a gateway, which generates:

           C               = "XY"
           ADMD            = "PTT"
           PRMD            = "Griddle MHS Providers"
           Organisation    = "Widget Corporation"
           Surname         = "Soap"
           Given Name      = "Joe"

   This is then routed to another gateway where the mapping is reversed
   to give:

           Joe.Soap@Widget.PTT.XY

   Here, use of the gateway is transparent.

   Mappings will only be symmetrical where mapping tables are defined.
   In other cases, the reversibility is more important, due to the (far
   too frequent) cases where RFC 822 and X.400 services are partitioned.

   The syntax may be used to source route.  THIS IS STRONGLY
   DISCOURAGED.  For example:

         X.400 -> RFC 822  -> X.400

         C             = "UK"
         ADMD          = "Gold 400"
         PRMD          = "UK.AC"
         "RFC-822"     = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"

   This will be sent to an arbitrary UK Academic Community gateway by
   X.400.  Then it will be sent by JNT Mail to another gateway
   determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria).  This will

   then derive the X.400 O/R Address:

           C             = "FR"
           ADMD          = "ATLAS"
           PRMD          = "Inria"
           PN.S          = "Duval"
           "Title"       = "Manager"

   Similarly:
   RFC 822 -> X.400 -> RFC 822

"/C=UK/ADMD=BT/PRMD=AC/RFC-822=jj(a)seismo.css.gov/"@monet.berkeley.edu

   This will be sent to monet.berkeley.edu by RFC 822, then to the AC
   PRMD by X.400, and then to jj@seismo.css.gov by RFC 822.

4.5.  Directory Names

   Directory Names are an optional part of O/R Name, along with O/R
   Address.  The RFC 822 addresses are mapped onto the O/R Address
   component. As there is no functional mapping for the Directory Name
   on the RFC 822 side, a textual mapping is used.  There is no
   requirement for reversibility in terms of the goals of this
   specification.  There may be some loss of functionality in terms of
   third party recipients where only a directory name is given, but this
   seems preferable to the significant extra complexity of adding a full
   mapping for Directory Names.

   Note:There is ongoing work on specification of a "user friendly"
        format for directory names.  If this is adopted as an
        internet standard, it will be recommended, but not required,
        for use here.

4.6.  MTS Mappings

   The basic mappings at the MTS level are:

   1) 822-MTS originator ->
                 MTS.PerMessageSubmissionFields.originator-name
      MTS.OtherMessageDeliveryFields.originator-name ->
                 822-MTS originator

   2) 822-MTS recipient ->
                 MTS.PerRecipientMessageSubmissionFields
      MTS.OtherMessageDeliveryFields.this-recipient-name ->
                 822-MTS recipient

   822-MTS recipients and return addresses are encoded as EBNF.822-

   address.

   The MTS Originator is always encoded as MTS.OriginatorName, which
   maps onto MTS.ORAddressAndOptionalDirectoryName, which in turn maps
   onto MTS.ORName.

4.6.1.  RFC 822 -> X.400

   From the 822-MTS Originator, use the basic ORAddress mapping, to
   generate MTS.PerMessageSubmissionFields.originator-name (MTS.ORName),
   without a DirectoryName.

   For recipients, the following settings are made for each component of
   MTS.PerRecipientMessageSubmissionFields.

   recipient-name
        This is derived from the 822-MTS recipient by the basic
        ORAddress mapping.

   originator-report-request
        This is be set according to content return policy, as
        discussed in Section 5.2.

   explicit-conversion
        This optional component is omitted, as this service is not
        needed

   extensions
        The default value (no extensions) is used

4.6.2.  X.400 -> RFC 822

   The basic functionality is to generate the 822-MTS originator and
   recipients.  There is information present on the X.400 side, which
   cannot be mapped into analogous 822-MTS services.  For this reason,
   new RFC 822 fields are added for the MTS Originator and Recipients.
   The information discarded at the 822-MTS level will be present in
   these fields. In some cases a (positive) delivery report will be
   generated.

4.6.2.1.  822-MTS Mappings

   Use the basic ORAddress mapping, to generate the 822-MTS originator
   (return address) from MTS.OtherMessageDeliveryFields.originator-name
   (MTS.ORName).  If MTS.ORName.directory-name is present, it is
   discarded.  (Note that it will be presented to the user, as described
   in 4.6.2.2).

   The 822-MTS recipient is conceptually generated from
   MTS.OtherMessageDeliveryFields.this-recipient-name.  This is done by
   taking MTS.OtherMessageDeliveryFields.this-recipient-name, and
   generating an 822-MTS recipient according to the basic ORAddress
   mapping, discarding MTS.ORName.directory-name if present.  However,
   if this model was followed exactly, there would be no possibility to
   have multiple 822-MTS recipients on a single message.  This is
   unacceptable, and so layering is violated.  The mapping needs to use
   the MTA level information, and map each value of
   MTA.PerRecipientMessageTransferFields.recipient-name, where the
   responsibility bit is set, onto an 822-MTS recipient.

4.6.2.2.  Generation of RFC 822 Headers

   Not all per-recipient information can be passed at the 822-MTS level.
   For this reason, two new RFC 822 headers are created, in order to
   carry this information to the RFC 822 recipient.  These fields are
   "X400-Originator:"  and "X400-Recipients:".

   The "X400-Originator:" field is set to the same value as the 822-MTS
   originator.  In addition, if
   MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName) contains
   MTS.ORName.directory-name then this Directory Name shall be
   represented in an 822.comment.

   Recipient names, taken from each value of
   MTS.OtherMessageDeliveryFields.this-recipient-name and
   MTS.OtherMessageDeliveryFields.other-recipient-names are made
   available to the RFC 822 user by use of the "X400-Recipients:" field.
   By taking the recipients at the MTS level, disclosure of recipients
   will be dealt with correctly.  However, this conflicts with a desire
   to optimise mail transfer.  There is no problem when disclosure of
   recipients is allowed. Similarly, there is no problem if there is
   only one RFC 822 recipient, as the "X400-Recipients field is only
   given one address.

   There is a problem if there are multiple RFC 822 recipients, and
   disclosure of recipients is prohibited.  Two options are allowed:

   1.   Generate one copy of the message for each RFC 822 recipient,
        with the "X400-Recipients field correctly set to the
        recipient of that copy.  This is functionally correct, but
        is likely to be more expensive.

   2.   Discard the per-recipient information, and insert a field:

                X400-Recipients: non-disclosure:;

        This is the recommended option.

   A third option of ignoring the disclosure flag is not allowed.  If
   any MTS.ORName.directory-name is present, it shall be represented in
   an 822.comment.

   If MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name
   is present, then there has been redirection, or there has been
   distribution list expansion.  Distribution list expansion is a per-
   message option, and the information associated with this is
   represented by the "DL-Expansion-History:" field descrined in Section
   5.3.6.  Other information is represented in an 822.comment associated
   associated with MTS.OtherMessageDeliveryFields.this-recipient-name,
   The message may be delivered to different RFC 822 recipients, and so
   several addresses in the "X400-Recipients:" field may have such
   comments.  The non-commented recipient is the RFC 822 recipient. The
   EBNF of the comment is:

           redirect-comment  =
                    [ "Originally To:" ] mailbox "Redirected"
                    [ "Again" ] "on" date-time
                    "To:"  redirection-reason

           redirection-reason =
                    "Recipient Assigned Alternate Recipient"
                    / "Originator Requested Alternate Recipient"
                    / "Recipient MD Assigned Alternate Recipient"

   It is derived from
   MTA.PerRecipientMessageTransferFields.extension.redirection-history.
   An example of this is:

   X400-Recipients: postmaster@widget.com (Originally To:
         sales-manager@sales.widget.com Redirected
         on Thu, 30 May 91 14:39:40 +0100 To: Originator Assigned
         Alternate Recipient postmaster@sales.widget.com Redirected
         Again on Thu, 30 May 91 14:41:20 +0100 To: Recipient MD
         Assigned Alternate Recipient)

   In addition, the following per-recipient services from
   MTS.OtherMessageDeliveryFields.extensions are represented in comments
   if they are used.  None of these services can be provided on RFC 822
   networks, and so in general these will be informative strings
   associated with other MTS recipients. In some cases, string values
   are defined.  For the remainder, the string value shall be chosen by
   the implementor.   If the parameter has a default value, then no
   comment shall be inserted when the parameter has that default value.

   requested-delivery-method

   physical-forwarding-prohibited
        "(Physical Forwarding Prohibited)".

   physical-forwarding-address-request
        "(Physical Forwarding Address Requested)".

   physical-delivery-modes

   registered-mail-type

   recipient-number-for-advice

   physical-rendition-attributes

   physical-delivery-report-request
        "(Physical Delivery Report Requested)".

   proof-of-delivery-request
        "(Proof of Delivery Requested)".

4.6.2.3.  Delivery Report Generation

   If MTA.PerRecipientMessageTransferFields.per-recipient-indicators
   requires a positive delivery notification, this shall be generated by
   the gateway.  Supplementary Information shall be set to indicate that
   the report is gateway generated.  This information shall include the
   name of the gateway generating the report.

4.6.3.  Message IDs (MTS)

   A mapping from 822.msg-id to MTS.MTSIdentifier is defined.  The
   reverse mapping is not needed, as MTS.MTSIdentifier is always mapped
   onto new RFC 822 fields.  The value of MTS.MTSIdentifier.local-part
   will facilitate correlation of gateway errors.

   To map from 822.msg-id, apply the standard mapping to 822.msg-id, in
   order to generate an MTS.ORAddress.  The Country, ADMD, and PRMD
   components of this are used to generate MTS.MTSIdentifier.global-
   domain-identifier.  MTS.MTSIdentifier.local-identifier is set to the
   822.msg-id, including the braces "<" and ">".   If this string is
   longer than MTS.ub-local-id-length (32), then it is truncated to this
   length.

   The reverse mapping is not used in this specification.  It would be
   applicable where MTS.MTSIdentifier.local-identifier is of syntax
   822.msg-id, and it algorithmically identifies MTS.MTSIdentifier.

4.7.  IPMS Mappings

   All RFC 822 addresses are assumed to use the 822.mailbox syntax.
   This includes all 822.comments associated with the lexical tokens of
   the 822.mailbox.  In the IPMS O/R Names are encoded as MTS.ORName.
   This is used within the  IPMS.ORDescriptor, IPMS.RecipientSpecifier,
   and IPMS.IPMIdentifier.  An asymmetrical mapping is defined between
   these components.

4.7.1.  RFC 822 -> X.400

   To derive IPMS.ORDescriptor from an RFC 822 address.

   1.   Take the address, and extract an EBNF.822-address.  This can
        be derived trivially from either the 822.addr-spec or
        822.route-addr syntax.  This is mapped to MTS.ORName as
        described above, and used as IMPS.ORDescriptor.formal-name.

   2.   A string shall be built consisting of (if present):

   -         The 822.phrase component if the 822.address is an
             822.phrase 822.route-addr construct.

   -         Any 822.comments, in order, retaining the parentheses.

        This string is then encoded into T.61 use a human oriented
        mapping (as described in Chapter 3).  If the string is not
        null, it is assigned to IPMS.ORDescriptor.free-form-name.

   3.   IPMS.ORDescriptor.telephone-number is omitted.

   If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier,
   IPMS.RecipientSpecifier.reply-request and
   IPMS.RecipientSpecifier.notification-requests are set to default
   values (none and false).

   If the 822.group construct is present, any included 822.mailbox is
   encoded as above to generate a separate IPMS.ORDescriptor.  The
   822.group is  mapped to T.61, and a IPMS.ORDescriptor with only an
   free-form-name component built from it.

4.7.2.  X.400 -> RFC 822

   Mapping from IPMS.ORDescriptor to RFC 822 address.  In the basic
   case, where IPMS.ORDescriptor.formal-name is present, proceed as
   follows.

   1.   Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as

        EBNF.822-address.

   2a.  If IPMS.ORDescriptor.free-form-name is present, convert it
        to ASCII (Chapter 3), and use this as the 822.phrase
        component of 822.mailbox using the 822.phrase 822.route-addr
        construct.

   2b.  If IPMS.ORDescriptor.free-form-name is absent.  If
        EBNF.822-address is parsed as 822.addr-spec use this as the
        encoding of 822.mailbox.  If EBNF.822-address is parsed as
        822.route 822.addr-spec, then a 822.phrase taken from
        822.local-part is added.

   3.   If IPMS.ORDescriptor.telephone-number is present, this is
        placed in an 822.comment, with the string "Tel ".  The
        normal international form of number is used.  For example:

                (Tel +44-1-387-7050)

   4.   If IPMS.ORDescriptor.formal-name.directory-name is present,
        then a text representation is placed in a trailing
        822.comment.

   5.   If IPMS.RecipientSpecifier.report-request has any non-
        default values, then an 822.comment "(Receipt Notification
        Requested)", and/or "(Non Receipt Notification Requested)",
        and/or "(IPM Return Requested)" is appended to the address.
        If both receipt and non-receipt notfications are requested,
        the comment relating to the latter may be omitted, to make
        the RFC 822 address cleaner.  The effort of correlating P1
        and P2 information is too great to justify the gateway
        sending Receipt Notifications.

   6.   If IPMS.RecipientSpecifier.reply-request is True, an
        822.comment "(Reply requested)"  is appended to the address.

   If IPMS.ORDescriptor.formal-name is absent, IPMS.ORDescriptor.free-
   form-name is converted to ASCII, and used as 822.phrase within the
   RFC 822 822.group syntax.  For example:

           Free Form Name ":" ";"

   Steps 3-6 are then followed.

4.7.3.  IP Message IDs

   There is a need to map both ways between 822.msg-id and
   IPMS.IPMIdentifier.  This allows for X.400 Receipt Notifications,

   Replies, and Cross References to reference an RFC 822 Message ID,
   which is preferable to a gateway generated ID.  A reversible and
   symmetrical mapping is defined.  This allows for good things to
   happen when messages pass multiple times across the X.400/RFC 822
   boundary.

   An important issue with messages identifiers is mapping to the exact
   form, as many systems use these ids as uninterpreted keys.  The use
   of table driven mappings is not always symmetrical, particularly in
   the light of alternative domain names, and alternative management
   domains.  For this reason, a purely algorithmic mapping is used.  A
   mapping which is simpler than that for addresses can be used for two
   reasons:

   -    There is no major requirement to make message IDs "natural"

   -    There is no issue about being able to reply to message IDs.
        (For addresses, creating a return path which works is more
        important than being symmetrical).

   The mapping works by defining a way in which message IDs generated on
   one side of the gateway can be represented on the other side in a
   systematic manner.  The mapping is defined so that the possibility of
   clashes is is low enough to be treated as impossible.

4.7.3.1.  822.msg-id represented in X.400

   IPMS.IPMIdentifier.user is omitted.  The IPMS.IPMIdentifier.user-
   relative-identifier is set to a printable string encoding of the
   822.msg-id with the angle braces ("<" and ">") removed.  The upper
   bound on this component is 64.  The options for handling this are
   discussed in Section 5.1.3.

4.7.3.2.  IPMS.IPMIdentifier represented in RFC 822

   The 822.domain of 822.msg-id is set to the value "MHS". The
   822.local-part of 822.msg-id is built as

           [ printablestring ] "*"  [ std-or-address ]

   with EBNF.printablestring being the IPMS.IPMIdentifier.user-
   relative-identifier, and std-or-address being an encoding of the
   IPMS.IPMIdentifier.user.  If necessary, the 822.quoted-string
   encoding is used.  For example:

   <"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>

4.7.3.3.  822.msg-id -> IPMS.IPMIdentifier

   If the 822.local-part can be parsed as:

           [ printablestring ] "*"  [ std-or-address ]

   and the 822.domain is "MHS", then this ID was X.400 generated.  If
   EBNF.printablestring is present, the value is assigned to
   IPMS.IPMIdentifier.user-relative-identifier.  If EBNF.std-or-address
   is present, the O/R Address components derived from it are used to
   set IPMS.IPMIdentifier.user.

   Otherwise, this is an RFC 822 generated ID.  In this case, set
   IPMS.IPMIdentifier.user-relative-identifier to a printable string
   encoding of the 822.msg-id without the angle braces.

4.7.3.4.  IPMS.IPMIdentifier -> 822.msg-id

   If IPMS.IPMIdentifier.user is absent, and IPMS.IPMIdentifier.user-
   relative-identifier mapped to ASCII and angle braces added parses as
   822.msg-id, then this is an RFC 822 generated ID.

   Otherwise, the ID is X.400 generated.  Use the
   IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form
   string.  Build the 822.local-part of the 822.msg-id with the syntax:

           [ printablestring ] "*"  [ std-or-address ]

   The printablestring is taken from IPMS.IPMIdentifier.user-relative-
   identifier.  Use 822.quoted-string if necessary.  The 822.msg-id is
   generated with this 822.local-part, and "MHS" as the 822.domain.

4.7.3.5.  Phrase form

   In "InReply-To:" and "References:", the encoding 822.phrase may be
   used as an alternative to 822.msg-id.  To map from 822.phrase to
   IPMS.IPMIdentifier, assign IPMS.IPMIdentifier.user-relative-
   identifier to the phrase.  When mapping from IPMS.IPMIdentifier for
   "In-Reply-To:" and "References:", if IPMS.IPMIdentifier.user is
   absent and IPMS.IPMIdentifier.user-relative-identifier does not parse
   as 822.msg-id, generate an 822.phrase rather than adding the domain
   MHS.

4.7.3.6.  RFC 987 backwards compatibility

   The mapping defined here is different to that used in RFC 987, as the
   RFC 987 mapping lead to changed message IDs in many cases.  Fixing
   the problems is preferable to retaining backwards compatibility.  An

   implementation of this standard is encouraged to recognise message
   IDs generated by RFC 987.  This is not required.

   RFC 987 generated encodings may be recognised as follows.  When
   mapping from X.400 to RFC 822, if the IPMS.IPMIdentifier.user-
   relative-identifier is "RFC-822" the id is RFC 987 generated. When
   mapping from RFC 822 to X.400, if the 822.domain is not "MHS", and
   the 822.local-part can be parsed as

           [ printablestring ] "*"  [ std-or-address ]

   then it is RFC 987 generated.  In each of these cases, it is
   recommended to follow the RFC 987 rules.

Chapter 5 - Detailed Mappings

   This chapter specifies  detailed mappings for the functions outlined
   in Chapters 1 and 2.  It makes extensive use of the notations and
   mappings defined in Chapters 3 and 4.

5.1.  RFC 822 -> X.400

5.1.1.  Basic Approach

   A single IP Message is generated from an RFC 822 message The RFC 822
   headers are used to generate the IPMS.Heading.  The IP Message will
   have one IA5 IPMS.BodyPart containing the RFC 822 message body.

   Some RFC 822 fields cannot be mapped onto a standard IPM Heading
   field, and so an extended field is defined in Section 5.1.2.  This is
   then used for fields which cannot be mapped onto existing services.

   The message is submitted to the MTS, and the services required can be
   defined by specifying MTS.MessageSubmissionEnvelope.  A few
   parameters of the MTA Abstract service are also specified, which are
   not in principle available to the MTS User.  Use of these services
   allows RFC 822 MTA level parameters to be carried in the analogous
   X.400 service elements.  The advantages of this mapping far outweigh
   the layering violation.

5.1.2.  X.400 Extension Field

   An IPMS Extension is defined:

        rfc-822-field HEADING-EXTENSION
                VALUE RFC822FieldList
                ::= id-rfc-822-field-list

        RFC822FieldList ::= SEQUENCE OF RFC822Field

        RFC822Field ::= IA5String

   The Object Identifier id-rfc-822-field-list is defined in Appendix D.

   To encode any RFC 822 Header using this extension, an RFC822Field
   element is built using the 822.field omitting the trailing CRLF
   (e.g., "Fruit-Of-The-Day: Kiwi Fruit"). Structured fields shall be
   unfolded.  There shall be no space before the ":".  The reverse
   mapping builds the RFC 822 field in a straightforward manner.  This
   RFC822Field is appended to the RFC822FieldList, which is added to the
   IPM Heading as an extension field.

5.1.3.  Generating the IPM

   The IPM (IPMS Service Request) is generated according to the rules of
   this section. The IPMS.IPM.body usually consists of one IPMS.BodyPart
   of type IPMS.IA5TextBodyPart with
   IPMS.IA5TextBodyPart.parameters.repertoire set to the default (ia5)
   which contains the body of the RFC 822 message.  The exception is
   where there is a "Comments:" field in the RFC 822 header.

   If no specific 1988 features are used, the IPM generated is encoded
   as content type 2.  Otherwise, it is encoded as content type 22.  The
   latter will always be the case if extension heading fields are
   generated.

   When generating the IPM, the issue of upper bounds must be
   considered.  At the MTS and MTA level, this specification is strict
   about enforcing upper bounds. Three options are available at the IPM
   level.  Use of any of these options conforms to this standard.

   1.   Ignore upper bounds, and generate messages in the natural
        manner.  This assumes that if any truncation is done, it
        will happen at the recipient UA.  This will maximise
        transfer of information, but is likely break some recipient
        UAs.

   2.   Reject any inbound message which would cause a message
        violating constraints to be generated.  This will be robust,
        but may prevent useful communication.

   3.   Truncate fields to the upper bounds specified in X.400.

        This will prevent problems with UAs which enforce upper
        bounds, but will sometimes discard useful information.

        If the Free Form name is truncated, it may lead to breaking
        RFC 822 comments, which will cause an awkward reverse
        mapping.

   These options have different advantages and disadvantages, and the
   choice will depend on the exact application of the gateway.

   The rest of this section concerns IPMS.IPM.heading (IPMS.Heading).
   The only mandatory component of IPMS.Heading is the
   IPMS.Heading.this-IPM (IPMS.IPMIdentifier).  A default is generated
   by the gateway.  With the exception of "Received:", the values of
   multiple fields are merged (e.g., If there are two "To:" fields, then
   the mailboxes of both are merged to generate a single list which is
   used in the IPMS.Heading.primary-recipients.  Information shall be
   generated from the standard RFC 822 Headers as follows:

   Date:
        Ignore (Handled at MTS level)

   Received:
        Ignore (Handled at MTA level)

   Message-Id:
        Mapped to IPMS.Heading.this-IPM.  For these, and all other
        fields containing 822.msg-id the mappings of Chapter 4 are
        used for each 822.msg-id.

   From:
        If Sender: is present, this is mapped to
        IPMS.Heading.authorizing-users.  If not, it is mapped to
        IPMS.Heading.originator.  For this, and other components
        containing addresses, the mappings of Chapter 4 are used for
        each address.

   Sender:
        Mapped to IPMS.Heading.originator.

   Reply-To:
        Mapped to IPMS.Heading.reply-recipients.

   To:  Mapped to IPMS.Heading.primary-recipients

   Cc:  Mapped to IPMS.Heading.copy-recipients.

   Bcc: Mapped to IPMS.Heading.blind-copy-recipients if there is at
        least one BCC:  recipient.  If there are no recipients in
        this field, it should be mapped to a zero length sequence.

   In-Reply-To:
        If there is one value, it is mapped to
        IPMS.Heading.replied-to-IPM, using the 822.phrase or
        822.msg-id mapping as appropriate.  If there are several
        values, they are mapped to IPMS.Heading.related-IPMs, along
        with any values from a "References:" field.

   References:
        Mapped to IPMS.Heading.related-IPMs.

   Keywords:
        Mapped onto a heading extension.

   Subject:
        Mapped to IPMS.Heading.subject.  The field-body uses the
        human oriented mapping referenced in Chapter 3 from ASCII to
        T.61.

   Comments:
        Generate an IPMS.BodyPart of type IPMS.IA5TextBodyPart with
        IPMS.IA5TextBodyPart.parameters.repertoire set to the
        default (ia5), containing the value of the fields, preceded
        by the string "Comments: ".  This body part shall precede
        the other one.

   Encrypted:
        Mapped onto a heading extension.

   Resent-*
        Mapped onto a heading extension.

        Note that it would be possible to use a ForwardedIPMessage
        for these fields, but the semantics are (arguably) slightly
        different, and it is probably not worth the effort.

   Other Fields

        In particular X-* fields, and "illegal" fields in common
        usage (e.g., "Fruit-of-the-day:") are mapped onto a heading
        extension, unless covered by another section or appendix of
        this specification.  The same treatment is applied to RFC
        822 fields where the content of the field does not conform
        to RFC 822 (e.g., a Date: field with unparseable syntax).

5.1.4.  Mappings to the MTS Abstract Service

   The MTS.MessageSubmissionEnvelope comprises
   MTS.PerMessageSubmissionFields, and

   MTS.PerRecipientMessageSubmissionFields.  The mandatory parameters
   are defaulted as follows.

   MTS.PerMessageSubmissionFields.originator-name
        This is always generated from 822-MTS, as defined in
        Chapter 4.

   MTS.PerMessageSubmissionFields.content-type
        Set to the value implied by the encoding of the IPM (2 or
        22).

   MTS.PerRecipientMessageSubmissionFields.recipient-name
        These will always be supplied from 822-MTS, as defined in
        Chapter 4.

   Optional components are omitted, and default components defaulted.
   This means that disclosure of recipients is prohibited and conversion
   is allowed.  There are two exceptions to the defaulting. For
   MTS.PerMessageSubmissionFields.per-message-indicators, the following
   settings are made:

   -    Alternate recipient is allowed, as it seems desirable to
        maximise the opportunity for (reliable) delivery.

   -    Content return request is set according to the issues
        discussed in Section 5.2.

   MTS.PerMessageSubmissionFields.original-encoded-information-types is
   a set of one element BuiltInEncodedInformationTypes.ia5-text.

   The MTS.PerMessageSubmissionFields.content-correlator is encoded as
   IA5String, and contains the Subject:, Message-ID:, Date:,  and

   To: fields (if present).  This  includes the strings "Subject:",
   "Date:", "To:", "Message-ID:", and appropriate folding.  This shall
   be truncated to MTS.ub-content-correlator-length (512) characters.
   In addition, if there is a "Subject:" field, the
   MTS.PerMessageSubmissionFields.content-identifier, is set to a
   printable string representation of the contents of it.   If the
   length of this string is greater than MTS.ub-content-id-length (16),
   it should be truncated to 13 characters and the string "..."
   appended. Both are used, due to the much larger upper bound of the
   content correlator, and that the content id is available in
   X.400(1984).

5.1.5.  Mappings to the MTA Abstract Service

   There is a need to map directly onto some aspects of the MTA Abstract

   service, for the following reasons:

   -    So the the MTS Message Identifier can be generated from the
        RFC 822 Message-ID:.

   -    So that the submission date can be generated from the
        822.Date.

   -    To prevent loss of trace information

   -    To prevent RFC 822/X.400 looping caused by distribution
        lists or redirects

   The following mappings are defined.

   Message-Id:
        If this is present, the
        MTA.PerMessageTransferFields.message-identifier is generated
        from it, using the mappings described in Chapter 4.

   Date:
        This is used to set the first component of
        MTA.PerMessageTransferFields.trace-information
        (MTA.TraceInformationElement).  The 822-MTS originator is
        mapped into an MTS.ORAddress, and used to derive
        MTA.TraceInformationElement.global-domain-identifier.  The
        optional components of
        MTA.TraceInformationElement.domain-supplied-information are
        omitted, and the mandatory components are set as follows:

          MTA.DomainSuppliedInformation.arrival-time
             This is set to the date derived from Date:

          MTA.DomainSuppliedInformation.routing-action
             Set to relayed.

        The first element of
        MTA.PerMessageTransferFields.internal-trace-information is
        generated in an analogous manner, although this can be
        dropped later in certain circumstances (see the procedures
        for "Received:").  The
        MTA.InternalTraceInformationElement.mta-name is derived from
        the 822.domain in the 822 MTS Originator address.

   Received:
        All RFC 822 trace is used to derive
        MTA.PerMessageTransferFields.trace-information and
        MTA.PerMessageTransferFields.internal-trace-information.

        Processing of Received: lines  follows processing of Date:,
        and is be done from the the bottom to the top of the RFC 822
        header (i.e., in chronological order).  When other trace
        elements are processed (X400-Received: in all cases and Via:
        if Appendix B is supported), the relative ordering shall be
        retained correctly.  The initial element of
        MTA.PerMessageTransferFields.trace-information will be
        generated already (from Date:), unless the message has
        previously been in X.400, when it will be derived from the
        X.400 trace information.

        Consider the Received: field in question.  If the "by"  part
        of the received is present, use it to derive an
        MTS.GlobalDomainIdentifier.  If this is different from the
        one in the last element of
        MTA.PerMessageTransferFields.trace-information
        (MTA.TraceInformationElement.global-domain-identifier)
        create a new MTA.TraceInformationElement, and optionally
        remove
        MTA.PerMessageTransferFields.internal-trace-information.
        This removal shall be done in cases where the message is
        being transferred to another MD where there is no bilateral
        agreement to preserve internal trace beyond the local MD.
        The trace creation is as for internal trace described below,
        except that no MTA field is needed.

        Then add a new element (MTA.InternalTraceInformationElement)
        to MTA.PerMessageTransferFields.internal-trace-information,
        creating this if needed.  This shall be done, even if
        inter-MD trace is created.  The
        MTA.InternalTraceInformationElement.global-domain-identifier
        is set to the value derived.  The
        MTA.InternalTraceInformationElement.mta-supplied-information
        (MTA.MTASuppliedInformation) is set as follows:

          MTA.MTASuppliedInformation.arrival-time
             Derived from the date of the Received: line

          MTA.MTASuppliedInformation.routing-action
             Set to relayed

        The MTA.InternalTraceInformationElement.mta-name is taken
        from the "by" component of the "Received:" field, truncated
        to MTS.ub-mta-name-length (32).  For example:

           Received: from computer-science.nottingham.ac.uk by
              vs6.Cs.Ucl.AC.UK via Janet with NIFTP  id aa03794;
              28 Mar 89 16:38 GMT

   Generates the string

           vs6.Cs.Ucl.AC.UK

   Note that before transferring the message to some ADMDs, additional
   trace stripping may be required, as the implied path through multiple
   MDs would violate ADMD policy.   This will depend on bilateral
   agreement with the ADMD.

5.1.6.  Mapping New Fields

   This specification defines a number of new fields for Reports,
   Notifications and IP Messages in Section 5.3.  As this specification
   only aims to preserve existing services, a gateway conforming to this
   specification does not need to map all of these fields to X.400.

   Two  extended fields must be mapped, in order to prevent looping.
   "DL-Expansion-History:" is mapped to

   MTA.PerMessageTransferFields.extensions.dl-expansion-history X400-
   Received: must be mapped to MTA.PerMessageTransferFields.trace-
   information and MTA.PerMessageTransferFields.internal-trace-
   information.  In cases where X400-Received: is present, the usual
   mapping of Date: to generate the first element of trace should not be
   done.   This is because the message has come from X.400, and so the
   first element of trace can be taken from the first X400-Received:.

   Some field that shall not be mapped, and should be discarded.  The
   following cannot be mapped back:

   -    Discarded-X400-MTS-Extensions:

   -    Message-Type:

   -    Discarded-X400-IPMS-Extensions:

   If Message-Type: is set to "Multiple Part", then the messge is
   encoded according to RFC 934, and this may be mapped on to the
   corresponding X.400 structures.

   The following may cause problems, due to other information not being
   mapped back (e.g., extension numbers), or due to changes made on the
   RFC 822 side due to list expansion:

   -    X400-Content-Type:

   -    X400-Originator:

   -    X400-Recipients:

   -    X400-MTS-Identifier:

   Other fields may be either discarded or mapped to X.400.  It is
   usually desirable and beneficial to do map, particularly to
   facilitate support of a message traversing multiple gateways.  These
   mappings may be onto MTA, MTS, or IPMS services.  The level of
   support for this reverse mapping should be indicated in the gateway
   conformace statement.

5.2.  Return of Contents

   It is not clear how widely supported the X.400 return of contents
   service will be.  Experience with X.400(1984) suggests that support
   of this service may not be universal.  As this service is expected in
   the RFC 822 world, two approaches are specified.  The choice will
   depend on the use of X.400 return of contents withing the X.400
   community being serviced by the gateway.

   In environments where return of contents is widely supported, content
   return can be requested as a service.  The content return service can
   then be passed back to the end (RFC 822) user in a straightforward
   manner.

   In environments where return of contents is not widely supported, a
   gateway must make special provision to handle return of contents.
   For every message passing from RFC 822 -> X.400, content return
   request will not be requested, and report request always will be.
   When the delivery report comes back, the gateway can note that the
   message has been delivered to the recipient(s) in question.  If a
   non-delivery report is received, a meaningful report (containing some
   or all of the original message) can be sent to the 822-MTS
   originator.  If no report is received for a recipient, a (timeout)
   failure notice shall be sent to the 822-MTS originator.  The gateway
   may retransmit the X.400 message if it wishes.  When this approach is
   taken, routing must be set up so that error reports are returned
   through the same MTA.  This approach may be difficult to use in
   conjunction with some routing strategies.

5.3.  X.400 -> RFC 822

5.3.1.  Basic Approach

   A single RFC 822 message is generated from the incoming IP Message,
   Report, or IP Notification.   All IPMS.BodyParts are mapped onto a
   single RFC 822 body.  Other services are mapped onto RFC 822 header
   fields.  Where there is no appropriate existing field, new fields are

   defined for IPMS, MTS and MTA services.

   The gateway mechanisms will correspond to MTS Delivery.  As with
   submission, there are aspects where the MTA (transfer) services are
   also used. In particular, there is an optimisation to allow for
   multiple 822-MTS recipients.

5.3.2.  RFC 822 Settings

   An RFC 822 Service requires to have a number of mandatory fields in
   the RFC 822 Header.  Some 822-MTS services mandate specification of
   an 822-MTS Originator.  Even in cases where this is optional, it is
   usually desirable to specify a value.  The following defaults are
   defined, which shall be used if the mappings specified do not derive
   a value:

   822-MTS Originator
        If this is not generated by the mapping (e.g., for a
        Delivery Report), a value pointing at a gateway
        administrator shall be assigned.

   Date:
        A value will always be generated

   From:If this is not generated by the mapping, it is assigned
        equal to the 822-MTS Originator.  If this is gateway
        generated, an appropriate 822.phrase shall be added.

   At least one recipient field
        If no recipient fields are generated, a field "To: list:;",
        shall be added.

   This will ensure minimal RFC 822 compliance.  When generating RFC 822
   headers, folding may be used.  It is recommended to do this,
   following the guidelines of RFC 822.

5.3.3.  Basic Mappings

5.3.3.1.  Encoded Information Types

   This mapping from MTS.EncodedInformationTypes is needed in several
   disconnected places.  EBNF is defined as follows:

           encoded-info    = 1#encoded-type

           encoded-type    = built-in-eit / object-identifier

           built-in-eit    = "Undefined"         ; undefined (0)

                           / "Telex"             ; tLX (1)
                           / "IA5-Text"          ; iA5Text (2)
                           / "G3-Fax"            ; g3Fax (3)
                           / "TIF0"              ; tIF0 (4)
                           / "Teletex"           ; tTX (5)
                           / "Videotex"          ; videotex (6)
                           / "Voice"             ; voice (7)
                           / "SFD"               ; sFD (8)
                           / "TIF1"              ; tIF1 (9)

   MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info.
   MTS.EncodedInformationTypes.non-basic-parameters is ignored.  Built
   in types are mapped onto fixed strings (compatible with X.400(1984)
   and RFC 987), and other types are mapped onto EBNF.object-identifier.

5.3.3.2.  Global Domain Identifier

   The following simple EBNF is used to represent
   MTS.GlobalDomainIdentifier:

           global-id = std-or-address

   This is encoded using the std-or-address syntax, for the attributes
   within the Global Domain Identifier.

5.3.4.  Mappings from the IP Message

   Consider that an IPM has to be mapped to RFC 822.  The IPMS.IPM
   comprises an IPMS.IPM.heading and IPMS.IPM.body.   The heading is
   considered first.  Some EBNF for new fields is defined:

        ipms-field = "Obsoletes" ":" 1#msg-id
                   / "Expiry-Date" ":" date-time
                   / "Reply-By" ":" date-time
                   / "Importance" ":" importance
                   / "Sensitivity" ":" sensitivity
                   / "Autoforwarded" ":" boolean
                   / "Incomplete-Copy" ":"
                   / "Language" ":" language
                   / "Message-Type" ":" message-type
                   / "Discarded-X400-IPMS-Extensions" ":" 1#oid

        importance      = "low" / "normal" / "high"

        sensitivity     = "Personal" / "Private" /

                               "Company-Confidential"

        language        = 2*ALPHA [ language-description ]
        language-description = printable-string

        message-type    = "Delivery Report"
                        / "InterPersonal Notification"
                        / "Multiple Part"

   The mappings and actions for the IPMS.Heading is now specified for
   each element.  Addresses, and Message Identifiers are mapped
   according to Chapter 4.  Other mappings are explained, or are
   straightforward (algorithmic).  If a field with addresses contains
   zero elements, it should be discarded, execpt for
   IPMS.Heading.blind-copy-recipients, which can be mapped onto BCC:
   (the only RFC 822 field which allows zero recipients).

   IPMS.Heading.this-IPM
        Mapped to "Message-ID:".

   IPMS.Heading.originator
        If IPMS.Heading.authorizing-users is present this is mapped
        to Sender:, if not to "From:".

   IPMS.Heading.authorizing-users
        Mapped to "From:".

   IPMS.Heading.primary-recipients
        Mapped to "To:".

   IPMS.Heading.copy-recipients
        Mapped to "Cc:".

   IPMS.Heading.blind-copy-recipients
        Mapped to "Bcc:".

   IPMS.Heading.replied-to-ipm
        Mapped to "In-Reply-To:".

   IPMS.Heading.obsoleted-IPMs
        Mapped to the extended RFC 822 field "Obsoletes:"

   IPMS.Heading.related-IPMs
        Mapped to "References:".

   IPMS.Heading.subject
        Mapped to "Subject:".  The contents are converted to ASCII
        (as defined in Chapter 3).  Any CRLF are not mapped, but are
        used as points at which the subject field must be folded.

   IPMS.Heading.expiry-time
        Mapped to the extended RFC 822 field "Expiry-Date:".

   IPMS.Heading.reply-time
        Mapped to the extended RFC 822 field "Reply-By:".

   IPMS.Heading.reply-recipients
        Mapped to "Reply-To:".

   IPMS.Heading.importance
        Mapped to the extended RFC 822 field "Importance:".

   IPMS.Heading.sensitivity
        Mapped to the extended RFC 822 field "Sensitivity:".

   IPMS.Heading.autoforwarded
        Mapped to the extended RFC 822 field "Autoforwarded:".

   The standard extensions (Annex H of X.420 / ISO 10021-7) are
   mapped as follows:

   incomplete-copy
        Mapped to the extended RFC 822 field "Incomplete-Copy:".

   language
        Mapped to the extended RFC 822 field "Language:", filling in
        the two letter code. The language-description may filled in
        with a human readable description of the language, and it is
        recommended to do this.

   If the RFC 822 extended header is found, this shall be mapped onto an
   RFC 822 header, as described in Section 5.1.2.

   If a non-standard extension is found, it shall be discarded, unless
   the gateway understands the extension and can perform an appropriate
   mapping onto an RFC 822 header field.  If extensions are discarded,
   the list is indicated in the extended RFC 822 field "Discarded-X400-
   IPMS-Extensions:".

   The IPMS.Body is mapped into the RFC 822 message body.  Each
   IPMS.BodyPart is converted to ASCII as follows:

   IPMS.IA5Text
        The mapping is straightforward (see Chapter 3).

   IPMS.MessageBodyPart
        The X.400 -> RFC 822 mapping  is recursively applied, to
        generate an RFC 822 Message.  If present, the
        IPMS.MessageBodyPart.parameters.delivery-envelope is used
        for the MTS Abstract Service Mappings.  If present, the
        IPMS.MessageBodyPart.parameters.delivery-time is mapped to
        the extended RFC 822 field "Delivery-Date:".

   Other
        If other body parts can be mapped to IA5, either by use of
        mappings defined in X.408 [CCITT88a], or by other reasonable
        mappings, this shall be done unless content conversion is
        prohibited.

   If some or all of the body parts cannot be converted there are three
   options.  All of these conform to this standard.  A different choice
   may be made for the case where no body part can be converted:

   1.   The first option is to reject the message, and send a non-
        delivery notification.  This must always be done if
        conversion is prohibited.

   2.   The second option is to map a missing body part to something
        of the style:

                *********************************

                There was a foobarhere

                The widget gateway ate it

                *********************************

        This will allow some useful information to be transferred.
        As the recipient is likely to be a human (IPMS), then
        suitable action will usually be possible.

   3.   Finally both may be done.  In this case, the supplementary
        information in the (positive) Delivery Report shall make
        clear that something was sent on to the recipient with
        substantial loss of information.

   Where there is more than one IPMS.BodyPart, the mapping defined by
   Rose and Stefferud in [Rose85a], is used to map the separate
   IPMS.BodyParts in the single RFC 822 message body.  If this is done,

   a "Message-Type:" field with value "Multiple part" shall be added,
   which will indicate to a receiving gateway that the message may be
   unfolded according to RFC 934.

   Note:There is currently work ongoing to produce an upgrade to RFC
        934, which also allows for support of body parts with non-
        ASCII content (MIME).  When this work is released as an RFC,
        this specification will be updated to refer to it instead
        for RFC 934.

   For backwards compatibility with RFC 987, the following procedures
   shall also be followed.  If there are two IA5 body parts, and the
   first starts with the string "RFC-822-Headers:" as the first line,
   then the remainder of this body part shall be appended to the RFC 822
   header.

   An example message, illustrating a number of aspects is given below.

Return-Path:<@mhs-relay.ac.uk:stephen.harrison@gosip-uk.hmg.gold-400.gb>
Received: from mhs-relay.ac.uk by bells.cs.ucl.ac.uk via JANET
          with NIFTP id <7906-0@bells.cs.ucl.ac.uk>;
          Thu, 30 May 1991 18:24:55 +0100
X400-Received: by mta "mhs-relay.ac.uk" in
               /PRMD=uk.ac/ADMD= /C=gb/; Relayed;
               Thu, 30 May 1991 18:23:26 +0100
X400-Received: by /PRMD=HMG/ADMD=GOLD 400/C=GB/; Relayed;
               Thu, 30 May 1991 18:20:27 +0100
Message-Type: Multiple Part
Date: Thu, 30 May 1991 18:20:27 +0100
X400-Originator: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
X400-MTS-Identifier:
     [/PRMD=HMG/ADMD=GOLD 400/C=GB/;PC1000-910530172027-57D8]
Original-Encoded-Information-Types: ia5, undefined
X400-Content-Type: P2-1984 (2)
Content-Identifier: Email Problems
From: Stephen.Harrison@gosip-uk.hmg.gold-400.gb (Tel +44 71 217 3487)
Message-ID: <PC1000-910530172027-57D8*@MHS>
To: Jim Craigie <NTIN36@gec-b.rutherford.ac.uk>
 (Receipt Notification Requested) (Non Receipt Notification Requested),
 Tony Bates <tony@ean-relay.ac.uk> (Receipt Notification Requested),
 Steve Kille <S.Kille@cs.ucl.ac.uk> (Receipt Notification Requested)
Subject: Email Problems
Sender: Stephen.Harrison@gosip-uk.hmg.gold-400.gb

------------------------------ Start of body part 1

Hope you gentlemen.......

Regards,

Stephen Harrison
UK GOSIP Project

------------------------------ Start of forwarded message 1

From: Urs Eppenberger <Eppenberger@verw.switch.ch>
Message-ID:
  <562*/S=Eppenberger/OU=verw/O=switch/PRMD=SWITCH/ADMD=ARCOM/C=CH/@MHS>
To: "Stephen.Harrison" <Stephen.Harrison@gosip-uk.hmg.gold-400.gb>
Cc: kimura@bsdarc.bsd.fc.nec.co.jp
Subject: Response to Email link

- ------------------------------ Start of body part 1

Dear Mr Harrison......

- ------------------------------ End of body part 1

------------------------------ End of forwarded message 1

5.3.5.  Mappings from an IP Notification

   A message is generated, with the following fields:

   From:
        Set to the IPMS.IPN.ipn-originator.

   To:  Set to the recipient from MTS.MessageSubmissionEnvelope.
        If there have been redirects, the original address should be
        used.

   Subject:
        Set to the string  "X.400 Inter-Personal Notification" for a
        receipt notification and to "X.400 Inter-Personal
        Notification (failure)" for a non-receipt notification.

   Message-Type:
        Set to "InterPersonal Notification"

   References:
        Set to IPMS.IPN.subject-ipm

   The following EBNF is defined for the body of the Message.  This
   format is defined to ensure that all information from an

   interpersonal notification is available to the end user in a uniform
   manner.

        ipn-body-format = ipn-description <CRLF>
                        [ ipn-extra-information <CRLF> ]
                        [ ipn-content-return ]

        ipn-description = ipn-receipt / ipn-non-receipt

        ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                 "was received at" receipt-time <CRLF> <CRLF>
                 "This notification was generated"
                 acknowledgement-mode <CRLF>
                 "The following extra information was given:" <CRLF>
                 ipn-suppl <CRLF>

        ipn-non-receipt "Your message to:"
                preferred-recipient <CRLF>
                ipn-reason

        ipn-reason = ipn-discarded / ipn-auto-forwarded

        ipn-discarded = "was discarded for the following reason:"
                        discard-reason <CRLF>

        ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                        [ "The following comment was made:"
                                auto-comment ]

        ipn-extra-information =
                 "The following information types were converted:"
                 encoded-info

        ipn-content-return = "The Original Message is not available"
                        / "The Original Message follows:"
                          <CRLF> <CRLF> message

        preferred-recipient = mailbox
        receipt-time        = date-time
        auto-comment        = printablestring
        ipn-suppl           = printablestring

        discard-reason     = "Expired" / "Obsoleted" /
                                "User Subscription Terminated"

        acknowledgement-mode = "Manually" / "Automatically"

   The mappings for elements of the common fields of IPMS.IPN
   (IPMS.CommonFields) onto this structure and the message header are:

   subject-ipm
        Mapped to "References:"

   ipn-originator
        Mapped  to "From:".

   ipn-preferred-recipient
        Mapped to EBNF.preferred-recipient

   conversion-eits
        Mapped to EBNF.encoded-info in EBNF.ipn-extra-information

   The mappings for elements of IPMS.IPN.non-receipt-fields
   (IPMS.NonReceiptFields) are:

   non-receipt-reason
        Used to select between EBNF.ipn-discarded and
        EBNF.ipn-auto-forwarded

   discard-reason
        Mapped to EBNF.discard-reason

   auto-forward-comment
        Mapped to EBNF.auto-comment

   returned-ipm
        This applies only to non-receipt notifications.
        EBNF.ipn-content-return should always be omitted for receipt
        notifications, and always be present in non-receipt
        notifications.  If present, the second option of
        EBNF.ipn-content-return is chosen, and an RFC 822 mapping of
        the message included.  Otherwise the first option is chosen.

   The mappings for elements of IPMS.IPN.receipt-fields
   (IPMS.ReceiptFields) are:

   receipt-time
        Mapped to EBNF.receipt-time

   acknowledgement-mode
        Mapped to EBNF.acknowledgement-mode

   suppl-receipt-info
        Mapped to EBNF.ipn-suppl

   An example notification is:

           From: Steve Kille <steve@cs.ucl.ac.uk>
           To: Julian Onions <jpo@computer-science.nottingham.ac.uk>
           Subject: X.400 Inter-personal Notification
           Message-Type: InterPersonal Notification
           References: <1229.614418325@UK.AC.NOTT.CS>
           Date: Wed, 21 Jun 89 08:45:25 +0100

           Your message to: Steve Kille <steve@cs.ucl.ac.uk>
           was automatically forwarded.
           The following comment was made:
                   Sent on to a random destination

           The following information types were converted: g3fax

5.3.6.  Mappings from the MTS Abstract Service

   This section describes the MTS mappings for User Messages (IPM and
   IPN).  This mapping is defined by specifying the mapping of
   MTS.MessageDeliveryEnvelope.  The following extensions to RFC 822 are
   defined to support this mapping:

        mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                  / "X400-Originator" ":" mailbox
                  / "X400-Recipients" ":" 1#mailbox
                  / "Original-Encoded-Information-Types" ":"
                                  encoded-info
                  / "X400-Content-Type" ":" mts-content-type
                  / "Content-Identifier" ":" printablestring
                  / "Priority" ":" priority
                  / "Originator-Return-Address" ":" 1#mailbox
                  / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                  / "Conversion" ":" prohibition
                  / "Conversion-With-Loss" ":" prohibition
                  / "Requested-Delivery-Method" ":"
                                  1*( labelled-integer )
                  / "Delivery-Date" ":" date-time
                  / "Discarded-X400-MTS-Extensions" ":"
                                   1#( oid / labelled-integer )

        prohibition     = "Prohibited" / "Allowed"

        mts-msg-id       = "[" global-id ";" *text "]"

        mts-content-type = "P2" /  labelled-integer
                        / object-identifer

        priority        = "normal" / "non-urgent" / "urgent"

   The mappings for each element of MTS.MessageDeliveryEnvelope can now
   be considered.

   MTS.MessageDeliveryEnvelope.message-delivery-identifier
        Mapped to the extended RFC 822 field "X400-MTS-Identifier:".

   MTS.MessageDeliveryEnvelope.message-delivery-time
        Discarded, as this time will be represented in an
        appropriate trace element.

   The mappings for elements of
   MTS.MessageDeliveryEnvelope.other-fields
   (MTS.OtherMessageDeliveryFields) are:

   content-type
        Mapped to the extended RFC 822 field "X400-Content-Type:".
        The string "P2" is retained for backwards compatibility with
        RFC 987. This shall not be generated, and either the
        EBNF.labelled-integer  or EBNF.object-identifier encoding
        used.

   originator-name
        Mapped to the 822-MTS originator, and to the extended RFC
        822 field "X400-Originator:".  This is described in
        Section 4.6.2.

   original-encoded-information-types
        Mapped to the extended RFC 822 field
        "Original-Encoded-Information-Types:".

   priority
        Mapped to the extended RFC 822 field "Priority:".

   delivery-flags
        If the conversion-prohibited bit is set, add an extended RFC
        822 field "Conversion:".

   this-recipient-name and other-recipient-names

   originally-intended-recipient-name
        The handling of these elements is described in
        Section 4.6.2.

   converted-encoded-information-types
        Discarded, as it will always be IA5 only.

   message-submission-time
        Mapped to Date:.

   content-identifier
        Mapped to the extended RFC 822 field "Content-Identifier:".

   If any extensions (MTS.MessageDeliveryEnvelope.other-
   fields.extensions) are present, and they are marked as critical for
   transfer or delivery, then the message shall be rejected.  The
   extensions (MTS.MessageDeliveryEnvelope.other-fields.extensions) are
   mapped as follows.

   conversion-with-loss-prohibited
     If set to
     MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited,
     then add the extended RFC 822 field "Conversion-With-Loss:".

   requested-delivery-method
        Mapped to the extended RFC 822 field
        "Requested-Delivery-Method:".

   originator-return-address
        Mapped to the extended RFC 822 field
        "Originator-Return-Address:".

   physical-forwarding-address-request
   physical-delivery-modes
   registered-mail-type
   recipient-number-for-advice
   physical-rendition-attributes
   physical-delivery-report-request
   physical-forwarding-prohibited

        These elements are only appropriate for physical delivery.
        They are represented as comments in the "X400-Recipients:"
        field, as described in Section 4.6.2.2.

   originator-certificate
   message-token
   content-confidentiality-algorithm-identifier
   content-integrity-check
   message-origin-authentication-check
   message-security-label
   proof-of-delivery-request

        These elements imply use of security services not available
        in the RFC 822 environment.  If they are marked as critical
        for transfer or delivery, then the message shall be
        rejected.  Otherwise they are discarded.

   redirection-history
        This is described in Section 4.6.2.

   dl-expansion-history
        Each element is mapped to the extended RFC 822 field
        "DL-Expansion-History:".  They shall be ordered in the
        message header, so that the most recent expansion comes
        first (same order as trace).

   If any MTS (or MTA) Extensions not specified in X.400 are present,
   and they are marked as critical for transfer or delivery, then the
   message shall be rejected.  If they are not so marked, they can
   safely be discarded.  The list of discarded fields shall be indicated
   in the extended header "Discarded-X400-MTS-Extensions:".

5.3.7.  Mappings from the MTA Abstract Service

   There are some mappings at the MTA Abstract Service level which are
   done for IPM and IPN.  These can be derived from
   MTA.MessageTransferEnvelope.  The reasons for the mappings at this
   level, and the violation of layering are:

   -    Allowing for multiple recipients to share a single RFC 822
        message

   -    Making the X.400 trace information available on the RFC 822
        side

   -    Making any information on deferred delivery available

   The 822-MTS recipients are calculated from the full list of X.400
   recipients.  This is all of the members of
   MTA.MessageTransferEnvelope.per-recipient-fields being passed through
   the gateway, where the responsibility bit is set.  In some cases, a
   different RFC 822 message would be calculated for each recipient, due
   to differing service requests for each recipient.  As discussed in
   4.6.2..2, this specification allows either for multiple messages to
   be generated, or for the per- recipient information to be discarded.

   The following EBNF is defined for extended RFC 822 headers:

        mta-field       = "X400-Received" ":" x400-trace
                        / "Deferred-Delivery" ":" date-time

                        / "Latest-Delivery-Time" ":" date-time

        x400-trace       = "by" md-and-mta ";"
                         [ "deferred until" date-time ";" ]
                         [ "converted" "(" encoded-info ")" ";" ]
                         [ "attempted" md-or-mta ";"  ]
                            action-list
                            ";" arrival-time

        md-and-mta       = [ "mta" mta "in" ]  global-id
        mta              = word
        arrival-time     = date-time

        md-or-mta        = "MD" global-id
                         / "MTA" mta

        Action-list      = 1#action
        action           = "Redirected"
                         / "Expanded"
                         / "Relayed"
                         / "Rerouted"

   Note the EBNF.mta is encoded as 822.word.  If the character set does
   no allow encoding as 822.atom, the 822.quoted-string encoding is
   used.

   If MTA.PerMessageTransferFields.deferred-delivery-time is present, it
   is used to generate a Deferred-Delivery: field.  For some reason,
   X.400 does not make this information available at the MTS level on
   delivery.  X.400 profiles, and in particular the CEN/CENELEC profile
   for X.400(1984) [Systems85a], specify that this element must be
   supported at the first MTA.  If it is not, the function may
   optionally be implemented by the gateway: that is, the gateway may
   hold the message until the time specified in the protocol element.
   Thus, the value of this element will usually be in the past.  For
   this reason, the extended RFC 822 field is primarily for information.

   Merge MTA.PerMessageTransferFields.trace-information, and
   MTA.PerMessageTransferFields.internal-trace-information to produce a
   single ordered trace list.  If Internal trace from other management
   domains has not been stripped, this may require complex interleaving.
   Where an element of internal trace and external trace are identical,
   except for the MTA in the internal trace, only the internal trace
   element shall be presented. Use this to generate a sequence of
   "X400-Received:" fields. The only difference between external trace
   and internal trace will be the extra MTA information in internal
   trace elements.

   When generating an RFC 822 message all trace fields (X400-Received
   and Received) shall be at the beginning of the header, before any
   other fields.  Trace shall be in chronological order, with the most
   recent element at the front of the message.  This ordering is
   determined from the order of the fields, not from timestamps in the
   trace, as there is no guarantee of clock synchronisation.  A simple
   example trace (external) is:

   X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ;
           Tue, 20 Jun 89 19:25:11 +0100

   A more complex example (internal):

   X400-Received: by mta "UK.AC.UCL.CS"
         in  /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ;
         deferred until  Tue, 20 Jun 89 14:24:22 +0100 ;
         converted (undefined, g3fax) ";" attempted /ADMD=Foo/C=GB/ ;
         Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +0100

5.3.8.  Mappings from Report Delivery

   Delivery reports are mapped at the MTS service level.  This means
   that only reports destined for the MTS user will be mapped.  Some
   additional services are also taken from the MTA service.

5.3.8.1.  MTS Mappings

   A Delivery Report service will be represented as
   MTS.ReportDeliveryEnvelope, which comprises of per-report-fields
   (MTS.PerReportDeliveryFields) and per-recipient-fields.

   A message is generated with the following fields:

   From:
        An administrator at the gateway system.  This is also the
        822-MTS originator.

   To:  A mapping of the
        MTA.ReportTransferEnvelope.report-destination-name.  This is
        also the 822-MTS recipient.

   Message-Type:
        Set to "Delivery Report".

   Subject:
        The EBNF for the subject line is:

         subject-line  = "Delivery-Report" "(" status ")"
                         [ "for" destination ]

         status        = "success" / "failure" / "success and failures"

         destination   = mailbox / "MTA" word

   The format of the body of the message is defined to ensure that all
   information is conveyed to the RFC 822 user in a consistent manner.
   The format is structured as if it was a message coming from X.400,
   with the description in one body part, and a forwarded message
   (return of content) in the second.  This structure is useful to the
   RFC 822 recipient, as it enables the original message to be
   extracted.  The first body part is structured as follows:

1.   A few lines giving keywords to indicate the original
     message.

2.   A human summary of the status of each recipient being
     reported on.

3.   A clearly marked section which contains detailed information
     extracted from the report.  This is marked clearly, as it
     will not be comprehensible to the average user.  It is
     retained, as it may be critical to diagnosing an obscure
     problem.

     This section may be omitted in positive DRs, and it is
     recommended that this is appropriate for most gateways.

        dr-body-format = dr-summary <CRLF>
                        dr-recipients <CRLF>
                        dr-administrator-info-envelope <CRLF>
                        dr-content-return

        dr-content-return = "The Original Message is not available"
             / "The Original Message follows:"

        dr-summary = "This report relates to your message:" <CRLF>
                        content-correlator <CRLF> <CRLF>
                     "of" date-time <CRLF> <CRLF>

        dr-recipients = *(dr-recipient <CRLF> <CRLF>)

        dr-recipient = dr-recip-success / dr-recip-failure

        dr-recip-success =
                        "Your message was successfully delivered to:"
                         mailbox "at" date-time

        dr-recip-failure = "Your message was not delivered to:"
                                mailbox <CRLF>
                        "for the following reason:" *word

        dr-administrator-info-envelope = 3*( "*" text <CRLF> )

        dr-administrator-info =
         "**** The following information is directed towards"
         "the local administrator" <CRLF>
         "**** and is not intended for the end user" <CRLF> <CRLF>
         "DR generated by:" report-point <CRLF>
         "at" date-time <CRLF> <CRLF>
         "Converted to RFC 822 at" mta <CRLF>
         "at" date-time <CRLF> <CRLF>
         "Delivery Report Contents:" <CRLF> <CRLF>
         drc-field-list <CRLF>
         "***** End of administration information"

        drc-field-list       = *(drc-field <CRLF>)

        drc-field = "Subject-Submision-Identifier" ":"
                                        mts-msg-id
                  / "Content-Identifier" ":" printablestring
                  / "Content-Type" ":" mts-content-type
                  / "Original-Encoded-Information-Types" ":"
                                encoded-info
                  / "Originator-and-DL-Expansion-History" ":"
                                dl-history
                  / "Reporting-DL-Name" ":" mailbox
                  / "Content-Correlator" ":" content-correlator
                  / "Recipient-Info" ":" recipient-info
                  / "Subject-Intermediate-Trace-Information" ":"
                                          x400-trace

        recipient-info  = mailbox "," std-or ";"
                    report-type
                    [ "converted eits" encoded-info ";" ]
                    [ "originally intended recipient"
                            mailbox "," std-or ";" ]
                    [ "last trace" [ encoded-info ] date-time ";" ]

                    [ "supplementary info" <"> printablestring <"> ";" ]
                    [ "redirection history" 1#redirection ";"
                    [ "physical forwarding address"
                                          printablestring ";" ]

        report-type     = "SUCCESS" drc-success
                        / "FAILURE" drc-failure

        drc-success     = "delivered at" date-time ";"
                        [ "type of MTS user" labelled-integer ";" ]

        drc-failure     = "reason" labelled-integer ";"
                        [ "diagnostic" labelled-integer ";" ]

        report-point = [ "mta" word "in" ] global-id
        content-correlator = *word
        dl-history = 1#( mailbox "(" date-time ")")

   The format is defined as a fixed definition of an the outer level
   (EBNF.dr-body-format).  The element EBNF.dr-administrator-info-
   envelope, provides a means of encapsulating a section of the header
   in a manner which is clear to the end user.  Each line of this
   section begins with "*".  Each element of EBNF.text within %EBNF.dr-
   administrator-info-envelope must not contain <CRLF>.  This is used to
   wrap up EBNF.dr-administrator-info, which will generate a sequenece
   of lines not starting with "*".  EBNF.drc-fields may be folded using
   the RFC 822 folding rules.

   The elements of MTS.ReportDeliveryEnvelope.per-report-fields are
   mapped as follows onto extended RFC 822 fields:

   subject-submission-identifier
        Mapped to EBNF.drc-field (Subject-Submission-Identifier)

   content-identifier
        Mapped to EBNF.drc-field (Content-Identifier).  This should
        also be used in EBNF.dr-summary if there is no Content
        Correlator present.

   content-type
        Mapped to EBNF.drc-field (Content-Type)

   original-encoded-information-types
        Mapped to EBNF.drc-field (Encoded-Info)

   The extensions from MTS.ReportDeliveryEnvelope.per-report-
   fields.extensions are mapped as follows:

   originator-and-DL-expansion-history
        Mapped to EBNF.drc-field (Originator-and-DL-Expansion-
        History)

   reporting-DL-name
        Mapped to EBNF.drc-field (Reporting-DL-Name)

   content-correlator
        Mapped to EBNF.content-correlator, provided that the
        encoding is IA5String (this will always be the case).  This
        is used in EBNF.dr-summary and EBNF.drc-field-list.  In the
        former, LWSP may be added, in order to improve the layout of
        the message.

   message-security-label reporting-MTA-certificate report-origin-
   authentication-check

        These security parameters will not be present unless there
        is an error in a remote MTA.  If they are present, they
        shall be discarded in preference to discarding the whole
        report.

   For each element of MTS.ReportDeliveryEnvelope.per-recipient-fields,
   a value of EBNF.dr-recipient, and an EBNF.drc-field (Recipient-Info)
   is generated.  The components are mapped as follows.

   actual-recipient-name
        Used to generate the first EBNF.mailbox and EBNF.std-or in
        EBNF.recipient-info.  Both RFC 822 and X.400 forms are
        given, as there may be a problem in the mapping tables.  It
        also generates the EBNF.mailbox in EBNF.dr-recip-success or
        EBNF.dr-recip-failure.

   report
        If it is MTS.Report.delivery, then set EBNF.dr-recipient to
        EBNF.dr-recip-success, and similarly set EBNF.report-type,
        filling in EBNF.drc-success.  If it is a failure, set
        EBNF.dr-recipient to EBNF.dr-recip-failure, making a human
        interpretation of the reason and diagnostic codes, and
        including any supplementary information.  EBNF.drc-failure
        is filled in systematically.

   converted-encoded-information-types
        Set EBNF.drc-field ("converted eits")

   originally-intended-recipient
        Set the second ("originally intended recipient") mailbox and
        std-or in EBNF.drc-field.

   supplementary-info
        Set EBNF.drc-field ("supplementary info"), and include this
        information in EBNF.dr-recip-failure.

   redirection-history
        Set EBNF.drc-field ("redirection history")

   physical-forwarding-address
        Set ENBF.drc-field ("physical forwarding address")

   recipient-certificate
        Discard

   proof-of-delivery
        Discard

   Any unknown extensions shall be discarded, irrespective of
   criticality.

   The original message, or an extract from it, shall be included in the
   delivery port if it is available.  The original message will usually
   be available at the gateway, as discussed in Section 5.2.  If the
   original message is available, but of erroneous format, a dump of the
   ASN.1 may be included.  This is recommended, but not required.

5.3.8.2.  MTA Mappings

   The single 822-MTS recipient is constructed from
   MTA.ReportTransferEnvelope.report-destination-name, using the
   mappings of Chapter 4.  Unlike with a user message, this information
   is not available at the MTS level.

   The following additional mappings are made:

   MTA.ReportTransferEnvelope.report-destination-name
        This is used to generate the To: field.

   MTA.ReportTransferEnvelope.identifier
        Mapped to the extended RFC 822 field "X400-MTS-Identifier:".
        It may also be used to derive a "Message-Id:" field.

   MTA.ReportTransferEnvelope.trace-information
        and

   MTA.ReportTransferEnvelope.internal-trace-information
        Mapped onto the extended RFC 822 field "X400-Received:", as
        described in Section 5.3.7.  The first element is also used
        to generate the "Date:" field, and the EBNF.report-point.

   MTA.PerRecipientReportTransferFields.last-trace-information
        Mapped to EBNF.recipient-info (last trace)

   MTA.PerReportTransferFields.subject-intermediate-trace-
        information Mapped to EBNF.drc-field (Subject-Intermediate-
        Trace-Information). These fields are ordered so that the
        most recent trace element comes first.

5.3.8.3.  Example Delivery Reports

   Example Delivery Report 1:

   Return-Path: <postmaster@cs.ucl.ac.uk>
   Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
      via Delivery Reports Channel id <27699-0@bells.cs.ucl.ac.uk>;
      Thu, 7 Feb 1991 15:48:39 +0000
   From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
   To: S.Kille@cs.ucl.ac.uk
   Subject: Delivery Report (failure) for H.Hildegard@bbn.com
   Message-Type: Delivery Report
   Date: Thu, 7 Feb 1991 15:48:39 +0000
   Message-ID: <"bells.cs.u.694:07.01.91.15.48.34"@cs.ucl.ac.uk>
   Content-Identifier: Greetings.

   ------------------------------ Start of body part 1

   This report relates to your message: Greetings.
           of Thu, 7 Feb 1991 15:48:20 +0000

   Your message was not delivered to
           H.Hildegard@bbn.com for the following reason:
           Bad Address
           MTA 'bbn.com' gives error message  (USER) Unknown user
           name in "H.Hildegard@bbn.com"

***** The following information is directed towards the local
***** administrator and is not intended for the end user
*
* DR generated by mta bells.cs.ucl.ac.uk
*         in /PRMD=uk.ac/ADMD=gold 400/C=gb/
*         at Thu, 7 Feb 1991 15:48:34 +0000

*
* Converted to RFC 822 at bells.cs.ucl.ac.uk
*         at Thu, 7 Feb 1991 15:48:40 +0000
*
 ..... continued on next page

* Delivery Report Contents:
*
* Subject-Submission-Identifier:
*      [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1803.665941698@UK.AC.UCL.CS>]
* Content-Identifier: Greetings.
* Subject-Intermediate-Trace-Information:
           /PRMD=uk.ac/ADMD=gold 400/C=gb/;
*          arrival Thu, 7 Feb 1991 15:48:20 +0000 action Relayed

* Subject-Intermediate-Trace-Information:
           /PRMD=uk.ac/ADMD=gold 400/C=gb/;
*          arrival Thu, 7 Feb 1991 15:48:18 +0000 action Relayed
* Recipient-Info: H.Hildegard@bbn.com,
*  /RFC-822=H.Hildegard(a)bbn.com/OU=cs/O=ucl
          /PRMD=uk.ac/ADMD=gold 400/C=gb/;
*         FAILURE reason Unable-To-Transfer (1);
*         diagnostic Unrecognised-ORName (0);
*         last trace (ia5) Thu, 7 Feb 1991 15:48:18 +0000;
*         supplementary info "MTA 'bbn.com' gives error message  (USER)
*         Unknown user name in "H.Hildegard@bbn.com"";
****** End of administration information

The Original Message follows:

------------------------------ Start of forwarded message 1

Received: from glenlivet.cs.ucl.ac.uk by bells.cs.ucl.ac.uk
  with SMTP inbound id <27689-0@bells.cs.ucl.ac.uk>;
  Thu, 7 Feb 1991 15:48:21 +0000
To: H.Hildegard@bbn.com
Subject: Greetings.
Phone: +44-71-380-7294
Date: Thu, 07 Feb 91 15:48:18 +0000
Message-ID: <1803.665941698@UK.AC.UCL.CS>
From: Steve Kille <S.Kille@cs.ucl.ac.uk>

Steve

------------------------------ End of forwarded message 1
Example Delivery Report 2:

Return-Path: <postmaster@cs.ucl.ac.uk>
Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
  via Delivery Reports Channel id <27718-0@bells.cs.ucl.ac.uk>;
  Thu, 7 Feb 1991 15:49:11 +0000
X400-Received: by mta bells.cs.ucl.ac.uk in
  /PRMD=uk.ac/ADMD=gold 400/C=gb/;
  Relayed; Thu, 7 Feb 1991 15:49:08 +0000
X400-Received: by /PRMD=DGC/ADMD=GOLD 400/C=GB/; Relayed;
  Thu, 7 Feb 1991 15:48:40 +0000
From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
To: S.Kille@cs.ucl.ac.uk
Subject: Delivery Report (failure) for
         j.nosuchuser@dle.cambridge.DGC.gold-400.gb
Message-Type: Delivery Report
Date: Thu, 7 Feb 1991 15:49:11 +0000
Message-ID: <"DLE/910207154840Z/000"@cs.ucl.ac.uk>
Content-Identifier: A useful mess...

This report relates to your message: A useful mess...
Your message was not delivered to
        j.nosuchuser@dle.cambridge.DGC.gold-400.gb
        for the following reason:
        Bad Address
        DG 21187: (CEO POA) Unknown addressee.

***** The following information is directed towards the local
***** administrator and is not intended for the end user
*
* DR generated by /PRMD=DGC/ADMD=GOLD 400/C=GB/
*         at Thu, 7 Feb 1991 15:48:40 +0000
*
* Converted to RFC 822 at bells.cs.ucl.ac.uk
*         at Thu, 7 Feb 1991 15:49:12 +0000
*
* Delivery Report Contents:
*
* Subject-Submission-Identifier:
*  [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1796.665941626@UK.AC.UCL.CS>]
* Content-Identifier: A useful mess...
* Recipient-Info: j.nosuchuser@dle.cambridge.DGC.gold-400.gb,
*     /I=j/S=nosuchuser/OU=dle/O=cambridge/PRMD=DGC/ADMD=GOLD 400/C=GB/;
*     FAILURE reason Unable-To-Transfer (1);
*     diagnostic Unrecognised-ORName (0);
*     supplementary info "DG 21187: (CEO POA) Unknown addressee.";
****** End of administration information

The Original Message is not available

5.3.9.  Probe

   This is an MTS internal issue.  Any probe shall be serviced by the
   gateway, as there is no equivalent RFC 822 functionality.  The value
   of the reply is dependent on whether the gateway could service an MTS
   Message with the values specified in the probe.  The reply shall make
   use of MTS.SupplementaryInformation to indicate that the probe was
   serviced by the gateway.

Appendix A - Mappings Specific to SMTP

   This Appendix is specific to the Simple Mail Transfer Protocol (RFC
   821).  It describes specific changes in the context of this protocol.
   When servicing a probe, as described in section 5.3.9, use may be
   made of the SMTP VRFY command to increase the accuracy of information
   contained in the delivery report.

Appendix B - Mappings specific to the JNT Mail

   This Appendix is specific to the JNT Mail Protocol.  It describes
   specific changes in the context of this protocol.

   1.  Introduction

      There are five aspects of a gateway which are JNT Mail Specific.
      These are each given a section of this appendix.

   2.  Domain Ordering

      When interpreting and generating domains, the UK NRS domain
      ordering shall be used, both in headers, and in text generated for
      human description.

   3.  Addressing

      A gateway which maps to JNT Mail should recognise the Domain
      Defined Attribute JNT-MAIL.  The value associated with this
      attribute should be interpreted according to the JNT Mail
      Specification.  This DDA shall never be generated by a gateway.
      For this reason, the overflow mechanism is not required.

   4.  Acknowledge-To:

      This field has no direct functional equivalent in X.400.  However,
      it can be supported to an extent, and can be used to improve X.400
      support.

      If an Acknowledge-To: field is present when going from JNT Mail to

      X.400, there are two different situations.  The first case is
      where there is one address in the Acknowledge-To: field, and it is
      equal to the 822-MTS return address.  In this case, the
      MTS.PerRecipientSubmissionFields.originator-request-report.report
      shall be set for each recipient, and the Acknowledge-To: field
      discarded.  Here, X.400 can provide the equivalent service.

      In all other cases two actions are taken.

         1. Acknowledgement(s) may be generated by the gateway.  The
            text of these acknowledgements shall indicate that they are
            generated by the gateway, and do not correspond to delivery.

         2. The Acknowledge-To: field shall be passed as an extension
            heading.

      When going from X.400 to JNT Mail, in cases where
      MTA.PerRecipientMessageTransferFields.per-recipient-indicators.
      originator-report bit is set for all recipients (i.e., there is a
      user request for a positive delivery report for every recipeint),
      generate an Acknowledge-To: field containing the
      MTS.OtherMessageDeliveryFields.originator-name.  Receipt
      notification requests are not mapped onto Acknowledge-To:, as no
      association can be guaranteed between IPMS and MTS level
      addressing information.

   5.  Trace

      JNT Mail trace uses the Via: syntax.  When going from JNT Mail to
      X.400, a mapping similar to that for Received:  is used. No
      MTS.GlobalDomainIdentifier of the site making the trace can be
      derived from the Via:, so a value for the gateway is used.  The
      trace text, including the "Via:", is unfolded, truncated to
      MTS.ub-mta-name-length (32), and mapped to
      MTA.InternalTraceInformationElement.mta-name.  There is no JNT
      Mail specific mapping for the reverse direction.

   6.  Timezone specification

      The extended syntax of zone defined in the JNT Mail Protocol shall
      be used in the mapping of UTCTime defined in Chapter 3.

   7.  Lack of 822-MTS originator specification

      In JNT Mail the default mapping of the
      MTS.OtherMessageDeliveryFields.originator-name is to the Sender:
      field.  This can cause a problem when going from X.400 to JNT Mail
      if the mapping of IPMS.Heading has already generated a Sender:

      field.  To overcome this, new extended JNT Mail field is defined.
      This is chosen to align with the JNT recommendation for
      interworking with full RFC 822 systems [Kille84b].

              original-sender     = "Original-Sender" ":" mailbox

      If an IPM has no IPMS.Heading.authorizing-users component and
      IPMS.Heading.originator.formal-name is different from
      MTS.OtherMessageDeliveryFields.originator-name, map
      MTS.OtherMessageDeliveryFields.originator-name, onto the Sender:
      field.

      If an IPM has a IPMS.Heading.authorizing-users component, and
      IPMS.Heading.originator.formal-name is different from
      MTS.OtherMessageDeliveryFields.originator-name,
      MTS.OtherMessageDeliveryFields.originator-name is mapped onto the
      Sender: field, and IPMS.Heading.originator mapped onto the
      Original-Sender: field.

      In other cases the MTS.OtherMessageDeliveryFields.originator-name,
      is already correctly represented.

Appendix C - Mappings specific to UUCP Mail

   Gatewaying of UUCP and X.400 is handled by first gatewaying the UUCP
   address into RFC 822 syntax (using RFC 976) and then gatewaying the
   resulting RFC 822 address into X.400.  For example, an X.400 address

           Country         US
           Organisation    Xerox
           Personal Name   John Smith

   might be expressed from UUCP as

           inthop!gate!gatehost.COM!/C=US/O=Xerox/PN=John.Smith/

   (assuming gate is a UUCP-ARPA gateway and gatehost.COM is an ARPA-
   X.400 gateway) or

           inthop!gate!Xerox.COM!John.Smith

   (assuming that Xerox.COM and /C=US/O=Xerox/ are equivalent.)

   In the other direction, a UUCP address Smith@ATT.COM, integrated into
   822, would be handled as any other 822 address.  A non-integrated
   address such as inthop!dest!user might be handled through a pair of
   gateways:

           Country         US
           ADMD            ATT
           PRMD            ARPA
           Organisation    GateOrg
           RFC-822         inthop!dest!user@gatehost.COM

   or through a single X.400 to UUCP gateway:

           Country         US
           ADMD            ATT
           PRMD            UUCP
           Organisation    GateOrg
           RFC-822         inthop!dest!user

Appendix D - Object Identifier Assignment

   An object identifier is needed for the extension IPMS element.  The
   following value shall be used.

   rfc-987-88 OBJECT IDENTIFIER ::=
       {ccitt data(9) pss(2342) ucl(234219200300) rfc-987-88(200)}

   id-rfc-822-field-list OBJECT IDENTIFIER ::= {rfc987-88 field(1)}

Appendix E - BNF Summary

        boolean = "TRUE" / "FALSE"

        numericstring = *DIGIT

        printablestring  = *( ps-char )
        ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                           / "," / "-" / "." / "/" / ":" / "=" / "?"
        ps-delim         = "(" / ")"
        ps-char          = ps-delim / ps-restricted-char

        ps-encoded       = *( ps-restricted-char / ps-encoded-char )
        ps-encoded-char  = "(a)"               ; (@)
                         / "(p)"               ; (%)
                         / "(b)"               ; (!)
                         / "(q)"               ; (")
                         / "(u)"               ; (_)
                         / "(l)"               ; "("
                         / "(r)"               ; ")"
                         / "(" 3DIGIT ")"

        teletex-string   = *( ps-char / t61-encoded )
        t61-encoded      = "{" 1* t61-encoded-char "}"
        t61-encoded-char = 3DIGIT

        teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]

        labelled-integer ::= [ key-string ] "(" numericstring ")"

        key-string      = *key-char
        key-char        = <a-z, A-Z, 0-9, and "-">

        object-identifier  ::= oid-comp object-identifier
                        | oid-comp

        oid-comp ::= [ key-string ] "(" numericstring ")"

        encoded-info    = 1#encoded-type

        encoded-type    = built-in-eit / object-identifier

        built-in-eit    = "Undefined"         ; undefined (0)
                        / "Telex"             ; tLX (1)
                        / "IA5-Text"          ; iA5Text (2)
                        / "G3-Fax"            ; g3Fax (3)
                        / "TIF0"              ; tIF0 (4)
                        / "Teletex"           ; tTX (5)
                        / "Videotex"          ; videotex (6)
                        / "Voice"             ; voice (7)
                        / "SFD"               ; sFD (8)
                        / "TIF1"              ; tIF1 (9)

        encoded-pn      = [ given "." ] *( initial "." ) surname

        given           = 2*<ps-char not including ".">

        initial         = ALPHA

        surname         = printablestring

        std-or-address  = 1*( "/" attribute "=" value ) "/"
        attribute       = standard-type
                        / "RFC-822"
                        / registered-dd-type

                        / dd-key "." std-printablestring
        standard-type   = key-string

        registered-dd-type
                        = key-string
        dd-key          = key-string

        value           = std-printablestring

        std-printablestring
                        = *( std-char / std-pair )
        std-char        = <"{", "}", "*", and any ps-char
                                        except "/" and "=">
        std-pair        = "$" ps-char

        dmn-or-address  = dmn-part *( "." dmn-part )
        dmn-part        = attribute "$" value
        attribute       = standard-type
                        / "~" dmn-printablestring
        value           = dmn-printablestring
                        / "@"
        dmn-printablestring =
                        = *( dmn-char / dmn-pair )
        dmn-char        = <"{", "}", "*", and any ps-char
                                                except ".">
        dmn-pair        = "\."

        global-id = std-or-address

        mta-field       = "X400-Received" ":" x400-trace
                        / "Deferred-Delivery" ":" date-time
                        / "Latest-Delivery-Time" ":" date-time

        x400-trace       = "by" md-and-mta ";"
                         [ "deferred until" date-time ";" ]
                         [ "converted" "(" encoded-info ")" ";" ]
                         [ "attempted" md-or-mta ";"  ]
                            action-list
                            ";" arrival-time

        md-and-mta       = [ "mta" mta "in" ]  global-id
        mta              = word
        arrival-time     = date-time

        md-or-mta        = "MD" global-id
                         / "MTA" mta

        Action-list      = 1#action
        action           = "Redirected"
                         / "Expanded"
                         / "Relayed"
                         / "Rerouted"

        dr-body-format = dr-summary <CRLF>
                        dr-recipients <CRLF>
                        dr-administrator-info-envelope <CRLF>
                        dr-content-return

        dr-content-return = "The Original Message is not available"
             / "The Original Message follows:"

        dr-summary = "This report relates to your message:" <CRLF>
                        content-correlator <CRLF> <CRLF>
                     "of" date-time <CRLF> <CRLF>

        dr-recipients = *(dr-recipient <CRLF> <CRLF>)

        dr-recipient = dr-recip-success / dr-recip-failure

        dr-recip-success =
                        "Your message was successfully delivered to:"
                         mailbox "at" date-time

        dr-recip-failure = "Your message was not delivered to:"
                                mailbox <CRLF>
                        "for the following reason:" *word

        dr-administrator-info-envelope = 3*( "*" text <CRLF> )

        dr-administrator-info =
         "**** The following information is directed towards"
         "the local administrator" <CRLF>
         "**** and is not intended for the end user" <CRLF> <CRLF>
         "DR generated by:" report-point <CRLF>
         "at" date-time <CRLF> <CRLF>
         "Converted to RFC 822 at" mta <CRLF>
         "at" date-time <CRLF> <CRLF>

         "Delivery Report Contents:" <CRLF> <CRLF>
         drc-field-list <CRLF>
         "***** End of administration information"

        drc-field-list       = *(drc-field <CRLF>)

        drc-field = "Subject-Submision-Identifier" ":"
                                        mts-msg-id
                  / "Content-Identifier" ":" printablestring
                  / "Content-Type" ":" mts-content-type
                  / "Original-Encoded-Information-Types" ":"
                                encoded-info
                  / "Originator-and-DL-Expansion-History" ":"
                                dl-history
                  / "Reporting-DL-Name" ":" mailbox
                  / "Content-Correlator" ":" content-correlator
                  / "Recipient-Info" ":" recipient-info
                  / "Subject-Intermediate-Trace-Information" ":"
                                          x400-trace

        recipient-info  = mailbox "," std-or ";"
                    report-type
                    [ "converted eits" encoded-info ";" ]
                    [ "originally intended recipient"
                            mailbox "," std-or ";" ]
                    [ "last trace" [ encoded-info ] date-time ";" ]
                    [ "supplementary info" <"> printablestring <"> ";" ]
                    [ "redirection history" 1#redirection ";"
                    [ "physical forwarding address"
                                          printablestring ";" ]

        report-type     = "SUCCESS" drc-success
                        / "FAILURE" drc-failure

        drc-success     = "delivered at" date-time ";"
                        [ "type of MTS user" labelled-integer ";" ]

        drc-failure     = "reason" labelled-integer ";"
                        [ "diagnostic" labelled-integer ";" ]

        report-point = [ "mta" word "in" ] global-id
        content-correlator = *word
        dl-history = 1#( mailbox "(" date-time ")")

        mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                  / "X400-Originator" ":" mailbox
                  / "X400-Recipients" ":" 1#mailbox
                  / "Original-Encoded-Information-Types" ":"
                                  encoded-info
                  / "X400-Content-Type" ":" mts-content-type
                  / "Content-Identifier" ":" printablestring
                  / "Priority" ":" priority
                  / "Originator-Return-Address" ":" 1#mailbox
                  / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                  / "Conversion" ":" prohibition
                  / "Conversion-With-Loss" ":" prohibition
                  / "Requested-Delivery-Method" ":"
                                  1*( labelled-integer )
                  / "Delivery-Date" ":" date-time
                  / "Discarded-X400-MTS-Extensions" ":"
                                   1#( oid / labelled-integer )

        prohibition     = "Prohibited" / "Allowed"

        mts-msg-id       = "[" global-id ";" *text "]"

        mts-content-type = "P2" /  labelled-integer
                        / object-identifer

        priority        = "normal" / "non-urgent" / "urgent"

        ipn-body-format = ipn-description <CRLF>
                        [ ipn-extra-information <CRLF> ]
                        [ ipn-content-return ]

        ipn-description = ipn-receipt / ipn-non-receipt

        ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                 "was received at" receipt-time <CRLF> <CRLF>
                 "This notification was generated"
                 acknowledgement-mode <CRLF>
                 "The following extra information was given:" <CRLF>
                 ipn-suppl <CRLF>

        ipn-non-receipt "Your message to:"
                preferred-recipient <CRLF>
                ipn-reason

        ipn-reason = ipn-discarded / ipn-auto-forwarded

        ipn-discarded = "was discarded for the following reason:"
                        discard-reason <CRLF>

        ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                        [ "The following comment was made:"
                                auto-comment ]

        ipn-extra-information =
                 "The following information types were converted:"
                 encoded-info

        ipn-content-return = "The Original Message is not available"
                        / "The Original Message follows:"
                          <CRLF> <CRLF> message

        preferred-recipient = mailbox
        receipt-time        = date-time
        auto-comment        = printablestring
        ipn-suppl           = printablestring

        discard-reason     = "Expired" / "Obsoleted" /
                                "User Subscription Terminated"

        acknowledgement-mode = "Manually" / "Automatically"

        ipms-field = "Obsoletes" ":" 1#msg-id
                   / "Expiry-Date" ":" date-time
                   / "Reply-By" ":" date-time
                   / "Importance" ":" importance
                   / "Sensitivity" ":" sensitivity
                   / "Autoforwarded" ":" boolean
                   / "Incomplete-Copy" ":"
                   / "Language" ":" language
                   / "Message-Type" ":" message-type
                   / "Discarded-X400-IPMS-Extensions" ":" 1#oid

        importance      = "low" / "normal" / "high"

        sensitivity     = "Personal" / "Private" /
                               "Company-Confidential"

        language        = 2*ALPHA [ language-description ]

        language-description = printable-string

        message-type    = "Delivery Report"
                        / "InterPersonal Notification"
                        / "Multiple Part"

        redirect-comment  =
                 [ "Originally To:" ] mailbox "Redirected"
                 [ "Again" ] "on" date-time
                 "To:"  redirection-reason

        redirection-reason =
                 "Recipient Assigned Alternate Recipient"
                 / "Originator Requested Alternate Recipient"
                 / "Recipient MD Assigned Alternate Recipient"

        subject-line  = "Delivery-Report" "(" status ")"
                        [ "for" destination ]

        status        = "success" / "failure" / "success and failures"

        destination   = mailbox / "MTA" word

        extended-heading =
            "Prevent-NonDelivery-Report" ":"
            / "Generate-Delivery-Report" ":"
            / "Alternate-Recipient" ":" prohibition
            / "Disclose-Recipients" ":"  prohibition
            / "Content-Return" ":" prohibition

Appendix F - Format of address mapping tables

   1.  Global Mapping Information

      The consistent operation of gateways which follow this
      specification relies of the existence of three globally defined
      mappings:

      1.   Domain Name Space -> O/R Address Space

      2.   O/R Address Space -> Domain Name Space

      3.   Domain Name Space -> O/R Address of preferred gateway

      All gateways conforming to this specification shall have access to
      these mappings.  The gateway may use standardised or private
      mechanisms to access this mapping information.

      One means of distributing this information is in three files.
      This appendix defines a format for these files.  Other
      standardised mechanisms to distribute the mapping information are
      expected.  In particular, mechanisms for using the Domain Name
      Scheme, and X.500 are planned.

      The definition of  global mapping information is being co-
      ordinated by the COSINE-MHS project, on behalf of the Internet and
      other X.400 and RFC 822 users.  For information on accessing this
      information contact:

           COSINE MHS Project Team
           SWITCH
           Weinbergstrasse 18
           8001 Zuerich
           Switzerland

           tel: +41 1 262 3143
           fax: +41 1 262 3151
           email:
           C=ch;ADMD=arcom;PRMD=switch;O=switch;OU=cosine-mhs;
           S=project-team
           or
           project-team@cosine-mhs.switch.ch

   2.  Syntax Definitions

      An address syntax is defined, which is compatible with the syntax
      used for 822.domains.  By representing the O/R addresses as
      domains, all lookups can be mechanically implemented as domain ->
      domain mappings.  This syntax defined is initially for use in
      table format, but the syntax is defined in a manner which makes it
      suitable to be adapted for  use with the  Domain Name Service.
      This syntax allows for a general representation of O/R addresses,
      so that it can be used in other applications.  Not all attributes
      are used in the table formats defined.

      To allow the mapping of null attributes  to be represented, the
      pseudo-value "@" (not a printable string character) is used to
      indicate omission of a level in the hierarchy.  This is distinct
      from the form including the element with no value, although a
      correct X.400 implementation will interpret both in the same
      manner.

      This syntax is not intended to be handled by users.

              dmn-or-address  = dmn-part *( "." dmn-part )
              dmn-part        = attribute "$" value
              attribute       = standard-type
                              / "~" dmn-printablestring
              value           = dmn-printablestring
                              / "@"
              dmn-printablestring =
                              = *( dmn-char / dmn-pair )
              dmn-char        = <"{", "}", "*", and any ps-char
                                                      except ".">
              dmn-pair        = "\."

      An example usage:

              ~ROLE$Big\.Chief.ADMD$ATT.C$US
              PRMD$DEC.ADMD$@.C$US

      The first example illustrates quoting of a ".", and the second
      omission of the ADMD level. There must be a strict ordering of all
      components in this table, with the most significant components on
      the RHS.   This allows the encoding to be treated as a domain.

      Various further restrictions are placed on the usage of dmn-or-
      address in the address space mapping tables.

      1.   Only C, ADMD, PRMD, O, and up to four OUs may be used.

      2.   No components shall be omitted from this hierarchy, although
           the hierarchy may terminate at any level.  If the mapping is
           to an omitted component, the "@" syntax is used.

   3.  Table Lookups

      When determining a match, there are aspects which apply to all
      lookups.  Matches are always case independent. The key for all
      three  tables is a domain. The longest possible match shall be
      obtained.  Suppose the table has two entries with the following
      keys:

              K.L
              J.K.L

      Domain "A.B.C" will not return any matches.  Domain "I.J.K.L" will
      match the entry "J.K.L:.

   4.  Domain -> O/R Address format

      The BNF is:

              domain-syntax "#" dmn-or-address "#"

      Note that the trailing "#" is used for clarity, as the dmn-or-
      address syntax might lead to values with trailing blanks.  Lines
      staring with "#" are comments.

              For example:
              AC.UK#PRMD$UK\.AC.ADMD$GOLD 400.C$GB#
              XEROX.COM#O$Xerox.ADMD$ATT.C$US#
              GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#

      A domain is looked up to determine the top levels of an O/R
      Address.  Components of the domain which are not matched are used
      to build the remainder of the O/R address, as described in Section
      4.3.4.

   5.  O/R Address -> Domain format

      The syntax of this table is:

              dmn-or-address "#" domain-syntax "#"

              For example:

              #
              # Mapping table
              #
              PRMD$UK\.AC.ADMD$GOLD 400.C$GB#AC.UK#

      The O/R Address is used to generate a domain key.  It is important
      to order the components correctly, and to fill in missing
      components in the hierarchy.  Use of this mapping is described in
      Section 4.3.2.

   6.  Domain -> O/R Address of Gateway table

      This uses the same format as the domain -> O/R address mapping.
      In this case, the two restrictions (omitted components and
      restrictions on components) do not apply.  Use of this mapping is
      described in Section 4.3.4.

Appendix G - Mapping with X.400(1984)

   This appendix defines modification to the  mapping for use with
   X.400(1984).

   The X.400(1984) protocols are a proper subset of X.400(1988).  When
   mapping from X.400(1984) to RFC 822, no changes to this specification
   are needed.

   When mapping from RFC 822 to X.400(1984), no use can be made of 1988
   specific features.   No use of such features is made at the MTS
   level.  One feature is used at the IPMS level, and this must be
   replaced by the RFC 987 approach.  All header information which would
   usually be mapped into the rfc-822-heading-list extension, together
   with any Comments: field in the RFC 822 header is mapped into a
   single IA5 body part, which is the first body part in the message.
   This body part will start with the string "RFC-822-Headers:" as the
   first line.  The headers then follow this line.  This specification
   requires correct reverse mapping of this format, either from 1988 or
   1984.

   In an environment where RFC 822 is of major importance, it may be
   desirable for downgrading to consider the case where the message was
   originated in an RFC 822 system, and mapped according to this
   specification.  The rfc-822-heading-list extension may be mapped
   according to this appendix.

   When parsing std-or, the following restrictions must be observed:

   -    Only the 84/88 attributes identified in the table in
        Section 4.2 are present.

   -    No teletex encoding is allowed.

   If an address violates this, it should be treated as an RFC 822
   address, which will usually lead to encoding as a DDA "RFC-822".

   It is possible that null attributes may be present in an O/R Address.
   This is not legal in 1988, except for ADMD where the case is
   explicitly described in Section 4.3.5.  Null attributes are
   deprecated (the attribute should be omitted), and should therefore be
   unusual.  However, some systems generate them and rely on them.
   Therefore, any null attribute shall be enoded using the std-or
   encoding (e.g., /O=/).

   If a non-Teletex Common Name (CN) is present, it should be mapped
   onto a Domain Defined Attribute "Common".  This is in line with RFC
   1328 on X.400 1988 to 1984 downgrading [Hardcastle-K92].

Appendix H - RFC 822 Extensions for X.400 access

   This appendix defines a number of optional mappings which may be
   provided to give access from RFC 822 to a number of X.400 services.
   These mappings are beyond the basic scope of this specification.
   There has been a definite demand to use extended RFC 822 as a
   mechanism to acccess X.400, and these extensions provide access to
   certain features.  If this functionality is provided, this appendix
   shall be followed.  The following headings are defined:

        extended-heading =
            "Prevent-NonDelivery-Report" ":"
            / "Generate-Delivery-Report" ":"
            / "Alternate-Recipient" ":" prohibition
            / "Disclose-Recipients" ":"  prohibition
            / "Content-Return" ":" prohibition

   Prevent-NonDelivery-Report and Generate-Delivery-Report allow setting
   of MTS.PerRecipientSubmissionFields.originator-report-request.  The
   setting will be the same for all recipients.

   Alternate-Recipient, Disclose-Recipients, and Content-Return allow
   for override of the default settings for MTS.PerMessageIndicators.

Appendix I - Conformance

   This appendix defines a number of options, which a conforming gateway
   should specify.  Conformance to this specification shall not be
   claimed if any of the mandatory features are not implemented.  In
   particular:

   -    Formats for all fields shall be followed.

   -    Formats for subject lines, delivery reports and IPNs shall
        be followed.   A system which followed the syntax, but
        translated text into a language other than english would be
        conformant.

   -    RFC 1137 shall not be followed when mapping to SMTP or to
        JNT Mail

   -    All mappings of trace shall be implemented.

   -    There must be a mechanism to access all three global
        mappings.

   A gateway should specify:

   -    Which 822-MTS protocols are supported.  The relevant
        appendices must be followed to claim support of a given
        protocol: SMTP (A); JNT Mail (B); UUCP (C).

   -    Which X.400 versions  are supported (84 and/or 88).

   -    The means by which it can access the global mappings.
        Currently, the tables of the formats define in  Appendix F
        is the only means available.

   -    The approach taken when upper bounds are exceeded at the IPM
        level  (5.1.3)

   -    The approach taken to return of contents (5.2)

   -    The approach taken to body parts which cannot be converted
        (5.3.4)

   -    The approach taken to multiple copies vs non-disclosure
        (4.6.2.2)

   The following are optional parts of this specification.  A conforming
   implementation should specify which of these it supports.

   -    Generation of extended RFC 822 fields is mandatory.
        Optionally, they may be parsed and mapped back to X.400.  A
        gateway should should indicate if this is done.

   -    Support for the extension mappings of Appendix H.

   -    Support for returning illegal format content in a delivery
        report

   -    Which address interpretation heuristics are supported
        (4.3.4.1)

   -    If RFC 987 generated message ids are handled in a backwards
        compatible manner (4.7.3.6)

Appendix J - Change History: RFC 987, 1026, 1138, 1148

   RFC 987 was the original document, and contained the key elements of
   this specification.  It was specific to X.400(1984).  RFC 1026
   specified a small number of necessary changes to RFC 987.

   RFC 1138 was based on the RFC 987 work.  It contained an editorial
   error, and was reissued a few months later as RFC 1148.  RFC 1148
   will be referred to here, as it is the document which is widely

   referred to elsewhere. The major goal of RFC 1148 was to upgrade RFC
   987 to X.400(1988).  It did this, but did not obsolete RFC 987, which
   was recommended for use with X.400(1984).  This appendix summarises
   the changes made in going from RFC 987 to RFC 1148.

   RFC 1148 noted the following about its upgrade from RFC 987:
   Unnecessary change is usually a bad idea.  Changes on the RFC 822
   side are avoided as far as possible,  so that RFC 822 users do not
   see arbitrary differences between systems conforming to this
   specification, and those following RFC 987.  Changes on the X.400
   side are minimised, but are more  acceptable, due to the mapping onto
   a new set of services and protocols.

   1.  Introduction

      The model has shifted from a protocol based mapping to a service
      based mapping.  This has increased the generality of the
      specification, and improved the model.  This change affects the
      entire document.

      A restriction on scope has been added.

   2.  Service Elements

      -    The new service elements of X.400 are dealt with.

      -    A clear distinction is made between origination and
           reception

   3.  Basic Mappings

      -    Add teletex support

      -    Add object identifier support

      -    Add labelled integer support

      -    Make PrintableString <-> ASCII mapping reversible

      -    The printable string mapping is aligned to the NBS mapping
           derived from RFC 987.

   4.  Addressing

      -    Support for new addressing attributes

      -    The message ID mapping is changed to not be table driven

   5.  Detailed Mappings

      -    Define extended IPM Header, and use instead of second body
           part for RFC 822 extensions

      -    Realignment of element names

      -    New syntax for reports, simplifying the header and
           introducing a mandatory body format (the RFC 987 header
           format was unusable)

      -    Drop complex autoforwarded mapping

      -    Add full mapping for IP Notifications, defining a body
           format

      -    Adopt an MTS Identifier syntax in line with the O/R Address
           syntax

      -    A new format for X400 Trace representation on the RFC 822
           side

   6.  Appendices

      -    Move Appendix on restricted 822 mappings to a separate RFC

      -    Delete Phonenet and SMTP Appendixes

Appendix K - Change History: RFC 1148 to this Document

   1.  General

      -    The scope of the document was changed to cover X.400(1984),
           and so obsolete RFC 987.

      -    Changes were made to allow usage to connect RFC 822 networks
           using X.400

      -    Text was tightened to be clear about optional and mandatory
           aspects

      -    A good deal of clarification

      -    A number of minor EBNF errors

      -    Better examples are given

      -    Further X.400 upper bounds are handled correctly

   2.  Basic Mappings

      -    The encoding of object identifier is changed slightly

   3.  Addressing

      -    A global mapping of domain to preferred gateway is
           introduced.

      -    An overflow mechanism is defined for RFC 822 addresses of
           greater than 128 bytes.

      -    Changes were made to improve compatability with the PDAM on
           writing O/R Addresses.

      +         The PD and Terminal Type keywords were aligned to the
                PDAM.  It is believed that minimal use has been made of
                the RFC 1148 keywords.

      +         P and A are allowed as alternate keys for PRMD and ADMD

      +         Where keywords are different, the PDAM keywords are
                alternatives on input.  This is mandatory.

   4.  Detailed Mappings

      -    The format of the Subject: lines is defined.

      -    Illegal use (repetition) of the heading EXTENSION is
           corrected, and a new object identifier assigned.

      -    The Delivery Report format is extensively revised in light
           of operational experience.

      -    The handling of redirects is significantly changed, as the
           previous mechanism did not work.

   5.  Appendices

      -    An SMTP appendix is added, allowing optional use of the VRFY
           command to improve probe information.

      -    Handling of JNT Mail Acknowledge-To is changed slightly.

      -    A DDA JNT-MAIL is allowed on input.

      -    The format definitions of Appendix F are explained further,
           and a third table definition added.

      -    An appendix on use with X.400(1984) is added.

      -    Optional extensions are defined to give RFC 822 access to
           further X.400 facilities.

      -    An appendix on conformance is added.

References

      CCITT88a.
           CCITT, "CCITT Recommendations X.408," Message Handling
           Systems: Encoded Information Type Conversion Rules, December
           1988.

      CCITT/ISO88a.
           CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1,"
           Message Handling: System and Service Overview , December
           1988.

      CCITT/ISO88b.
           CCITT/ISO, "CCITT Recommendations X.420/ ISO IS 10021-7,"
           Message Handling Systems: Interpersonal Messaging System,
           December 1988.

      CCITT/ISO88c.
           CCITT/ISO, "CCITT Recommendations X.411/ ISO IS 10021-4,"
           Message Handling Systems: Message Transfer System: Abstract
           Service Definition and Procedures, December 1988.

      CCITT/ISO88d.
           CCITT/ISO, "Specification of Abstract Syntax Notation One
           (ASN.1)," CCITT Recommendation X.208 / ISO IS 8824, December
           1988.

      CCITT/ISO91a.
           CCITT/ISO, "Representation of O/R Addresses for Human
           Usage," PDAM to CCITT X.401 / ISO/IEC 10021-2, February
           1991.

      Crocker82a.
           Crocker, D., "Standard of the Format of ARPA Internet Text
           Messages," RFC 822, UDEL, August 1982.

      Hardcastle-K92.
           Hardcastle-Kille, S., "X.400 1988 to 1984 downgrading," RFC
           1328, UCL, May 1992.

      Horton86a.
           Horton, M., "UUCP Mail Interchange Format Standard," RFC
           976, February 1986.

      Kille84b.
           Kille, S., "Gatewaying between RFC 822 and JNT Mail," JNT
           Mailgroup Note 15, May 1984.

      Kille84a.
           Kille, S., (Editor), JNT Mail Protocol (revision 1.0), Joint
           Network Team, Rutherford Appleton Laboratory, March 1984.

      Kille86a.
           Kille, S., "Mapping Between X.400 and RFC 822," UK Academic
           Community Report (MG.19) / RFC 987, June 1986.

      Kille87a.
           Kille, S., "Addendum to RFC 987," UK Academic Community
           Report (MG.23) / RFC 1026, August 1987.

      Kille89a.
           Kille, S., "A String Encoding of Presentation Address," UCL
           Research Note 89/14, March 1989.

      Kille89b.
           Kille, S., "Mapping between full RFC 822 and RFC 822 with
           restricted encoding," RFC 1137, October 1989.

      Kille90a.
           Kille, S., "Mapping Between X.400(1988) / ISO 10021 and RFC
           822," RFC 1148, March 1990.

      Larmouth83a.
           Larmouth, J., "JNT Name Registration Technical Guide,"
           Salford University Computer Centre, April 1983.

      Postel84a.
           Postel J., and J. Reynolds, "Domain Requirements," RFC 920,
           USC/Information Sciences Institute, October 1984.

      Postel82a.
           Postel, J., "Simple Mail Transfer Protocol", RFC 821,
           USC/Information Sciences Institute, August 1982.

      Rose85a.
           Rose M., and E. Stefferud, "Proposed Standard for Message
           Encapsulation," RFC 934, January 1985.

      Systems85a.
           CEN/CENELEC/Information Technology/Working Group on Private
           Message Handling Systems, "FUNCTIONAL STANDARD A/3222,"
           CEN/CLC/IT/WG/PMHS N 17, October 1985.

SECURITY CONSIDERATIONS

   Security issues are not discussed in this memo.

AUTHOR'S ADDRESS

   Steve Hardcastle-Kille
   Department of Computer Science
   University College London
   Gower Street
   WC1E 6BT
   England

   Phone: +44-71-380-7294
   EMail: S.Kille@CS.UCL.AC.UK

 

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