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RFC 987 - Mapping between X.400 and RFC 822


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UCL Technical Report 120
Mailgroup Note 19

Network Working Group                                         S.E. Kille
Request for Comments: 987                      University College London
                                                               June 1986

                   Mapping between X.400 and RFC 822

Status of This Memo

   This RFC suggests a proposed protocol for the ARPA-Internet
   community, and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

   This document describes a set of mappings which will enable
   interworking between systems operating the CCITT X.400 (1984) series
   of protocols [CCITT84a], 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 specification should be used when this mapping is performed on
   the ARPA-Internet or in the UK Academic Community.  This
   specification may be modified in the light of implementation
   experience, but no substantial changes are expected.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Chapter 1 -- Overview

   1.1.  X.400

      The X.400 series protocols have been defined by CCITT to provide
      an Interpersonal Messaging Service (IPMS), making use of a store
      and forward Message Transfer Service.  It is expected that this
      standard will be implemented very widely.  As well as the base
      standard (X.400), work is underway on various functional standards
      of profiles which specify how X.400 will be used in various
      communities.  Many of the major functional standards (e.g. from
      CEPT, CEN/CENELEC, and NBS) are likely to be similar.  Some of the
      decisions in this document are in the light of this work.  No
      reference is given, as these documents are not currently stable.

   1.2.  RFC 822

      RFC 822 evolved as a messaging standard on the DARPA (the US
      Defense Advanced Research Projects Agency) Internet.  It is
      currently used on the ARPA-Internet 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 a
      domain name system and a distributed name service [Postel84a].
      RFC 822, or protocols derived from RFC 822 are used in a number of
      other networks.  In particular:

         UUCP Networks

            UUCP is the UNIX to UNIX CoPy protocol <0>, 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 are likely to
            use domains which conform to RFC 920, but not the
            corresponding domain nameservers [Horton86a].

         CSNET

            Some portions of CSNET will follow the ARPA-Internet
            protocols. The dialup portion of CSNET uses the Phonenet
            protocols as a replacement for RFC 821.  This portion is
            likely to use domains which conform to RFC 920, but not the
            corresponding domain nameservers.

         BITNET

            Some parts of BITNET use RFC 822 related protocols, with
            EBCDIC encoding.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         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 X.400 systems.  This
      will be a requirement, even in cases where communities intend to
      make a transition to use of X.400, where conversion will be needed
      to ensure a smooth service transition.  It is expected that there
      will be more than one gateway <1>, and this specification will
      enable them to behave in a consistent manner.  These gateways are
      sometimes called mail relays.  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.

         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

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

              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.

   1.5.  Gatewaying Model

      1.5.1.  X.400

         The CCITT X.400 series recommendations specify a number of
         services and protocols.  The services are specified in X.400.
         Two of these services are fundamental to this document:

            1.   The Message Transfer Service, which can be provided by
                 either the P1 or P3 protocols, which are  specified in
                 X.411 [CCITT84b]. This document talks in terms of P1,
                 but the mappings are equally applicable to P3.

            2.   The Interpersonal Messaging Service (IPMS), which is
                 provided by the P2 protocol specified in X.420
                 [CCITT84c].

         This document considers only IPMS, and not of any other usage
         of the Message Transfer Service.  This is reasonable, as
         RFC 822, broadly speaking, provides a service corresponding to
         IPMS, and no services other than IPMS have been defined over
         the Message Transfer Service. As none of the RTS (Reliable
         Transfer Service) service elements is available to the IPMS
         user, this level and lower levels are of no concern in this
         gatewaying specification.  Note that in this memo "IP" means
         "InterPersonal" (not Internet Protocol).

         The Message Transfer Service defines an end-to-end service over
         a series of Message Transfer Agents (MTA).  It also defines a
         protocol, P1, which is used between a pair of MTAs.  This
         protocol is simply a file format (Message Protocol Data Unit,
         or MPDU), transferred between two MTAs using the RTS.  There
         are three types of MPDU:

            User MPDU

               This contains envelope information, and uninterpreted
               contents. The envelope includes an ID, an originator, a

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

               list of recipients, and trace information.  It is used to
               carry data for higher level services.

            Probe

               This contains only envelope information.  It is used to
               determine whether a User UMPDU could be delivered to a
               given O/R (originator/recipient) name.

            Delivery Report

               This contains envelope information, and specified
               contents.  It is used to indicate delivery success or
               failure of a User or Probe MPDU over the Message Transfer
               Service.

         IPMS (P2) specifies two content types for the P1 User MPDU
         (User Agent Protocol Data Units or UAPDU):

            Interpersonal Message (IM-UAPDU)

               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 header contains end to end user
               information, such as subject, primary recipients (To:),
               and priority.  The validity of these fields is not
               guaranteed by the Message Transfer Service.  This
               provides the basic IPMS.

            Status Report (SR-UAPDU)

               This UAPDU has defined contents.  It is used to indicate
               that a message has been received by a User Agent.  It
               does not have to be implemented.

      1.5.2.  RFC 822

         RFC 822 is based on the assumption that there is an underlying
         service, which is here called the 822-P1 service.  The 822-P1
         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.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         It is possible to achieve 2) within the RFC 822 header.  Some
         822-P1 protocols, in particular SMTP, can provide additional
         functionality, but as these are neither mandatory in SMTP, nor
         available in other 822-P1 protocols, they are not considered
         here.  Details of aspects specific to a number of 822-P1
         protocols are given in appendices B to E.  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
         header elements, although some are analogous to P1 envelope
         elements.

      1.5.3.  The Gateway

         Given this functional description of the two protocols, the
         functional nature of a gateway can now be considered.  It would
         be elegant to consider the 822-P1 service mapping onto P1 and
         RFC 822 mapping onto P2, but reality just does not fit.
         Therefore one must consider that P1 or P1 + P2 on one side are
         mapped into RFC 822 + 822-P1 on the other in a slightly tangled
         manner.  The details of the tangle will be made clear in
         chapter 5.  The following basic mappings are thus proposed.
         When going from RFC 822 to X.400, an RFC 822 message and the
         associated 822-P1 information is always mapped into an IM-UAPDU
         and the associated P1 envelope.  Going from X.400 to RFC 822,
         an RFC 822 message and the associated 822-P1 information may be
         derived from:

            1.   A Delivery Report MPDU

            2.   An SR-UAPDU and the associated P1 envelope.

            3.   An IM-UAPDU and the associated P1 envelope.

         Probe MPDUs must be processed by the gateway - this is
         discussed in chapter 5.  Any other User MPDUs are not mapped by
         the gateway, and should be rejected at the gateway.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   1.6.  Document Structure

      This document has five chapters:

         1.   Overview - this document.

         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.   Protocol Elements - This describes the details of all
              other mappings.

      There are also six appendices:

         A.   Quoted String Encodings.

         B.   Mappings Specific to JNT Mail.

         C.   Mappings Specific to Internet Mail.

         D.   Mappings Specific to Phonenet Mail.

         E.   Mappings Specific to UUCP Mail.

         F.   Format of Address Tables.

   1.7.  Acknowledgements

      This document is eclectic, and credit should be given:

         -    Study of the EAN X.400 system code which performs this
              function [Neufeld85a].  Some detailed clarification was
              made by the DFN report on EAN [Bonacker85a].

         -    An unpublished ICL report, which considered a subset of
              the problem [ICL84a].

         -    A document by Marshall Rose [Rose85a].

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         -    A document by Mark Horton [Horton85a].  The string
              encodings of chapter 3 were derived directly from this
              work, as is much of chapter 4.

         -    Discussion on a number of electronic mailing lists.

         -    Meetings in the UK and the US.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Chapter 2 -- Service Elements

   RFC 822 and X.400 provide a number of services to the end user.  This
   document 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.

   When a service element is described as supported, this means that
   when this service element is specified by a message originator for a
   recipient behind a gateway, that it is mapped by the gateway to
   provide the service implied by the element.  For example, 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.
   Support implies:

      -    Semantic correspondence.

      -    No loss of information.

      -    Any actions required by the service element.

   For some services, the corresponding protocol elements map well, and
   so the service can be fully provided.  In other cases, the service
   cannot be provided, as there is a complete mismatch.  In the
   remaining cases, the service can be partially fulfilled.  The level
   of partial support is summarised.

      NOTE:  It should be clear that support of service elements on
      reception is not a gatewaying issue.  It is assumed that all
      outbound messages are fully conforming to the appropriate
      standards.

   2.1.  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.  A mechanism
      of mapping used in several cases, is to place the text of the
      header into the body of the IP Message.  This can usually be
      regarded as partial support, as it allows the information to be
      conveyed to the end user even though there is no corresponding
      X.400 protocol element.  Support for the various service elements
      (headers) is now listed.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Date:

            Supported.

         From:

            Supported.  For messages where there is also a sender field,
            the mapping is to "Authorising Addresses", 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 in msg-id form.  Other
            cases are passed in the message text.

         References:

            Supported.

         Keywords:

            Passed in the message text.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Subject:

            Supported.

         Comments:

            Passed in the message text.

         Encrypted:

            Passed in the message text.  This may not be very useful.

         Resent-*

            Passed in the message text.  In principle, these could be
            supported in a fuller manner, but this is not suggested.

         Other Fields

            In particular X-* fields, and "illegal" fields in common
            usage (e.g. "Fruit-of-the-day:") are passed in the message
            text.

   2.2.  X.400

      When mapping from X.400 to RFC 822, it is not proposed to map any
      elements into the body of an RFC 822 message.  Rather, 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 almost supported.  Chapter 5
      describes how to map these new headers in both directions.  Other
      elements are provided, in part, by the gateway as they cannot be
      provided by RFC 822.  Some service elements are are marked N/A
      (not applicable).  These elements are only applicable to User
      Agent / Message Transfer Agent interaction and have no end-to-end
      implication. These elements do not need to be mapped by the
      gateway.

      2.2.1.  Message Transfer Service Elements

         Access Management

            N/A.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Content Type Indication

            Not mapped.  As it can only have one value (P2), there is
            little use in creating a new RFC 822 header field, unless it
            was to distinguish delivery reports.

         Converted Indication

            Supported by a new RFC 822 header.

         Delivery Time Stamp Indication

            N/A.

         Message Identification

            Supported, by use of a new RFC 822 header.  This new header
            is required, as X.400 has two message-ids whereas RFC 822
            has only one.

         Non-delivery Notification

            Not supported, although in general an RFC 822 system will
            return errors as IP messages.  In other elements, this
            pragmatic result is treated as effective support of this
            service element.

         Original Encoded Information Types Indication

            Supported as a new RFC 822 header.

         Registered Encoded Information Types

            N/A.

         Submission Time Stamp Indication

            Supported.

         Alternate Recipient Allowed

            Not supported.  Any value is ignored by the gateway.

         Deferred Delivery

            Support is optional.  The framework is provided so that
            messages may be held at the gateway.  However, a gateway

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            following this specification does not have to do this.  This
            is in line with the emerging functional standards.

         Deferred Delivery Cancellation

            Supported.

         Delivery Notification

            Supported at gateway.  Thus, a notification is sent by the
            gateway to the originator  <2>.

         Disclosure of Other Recipients

            Supported by use of a new RFC 822 header.

         Grade of Delivery Selection

            Supported as a new RFC 822 header.  In general, this will
            only be for user information in the RFC 822 world.

         Multi-Destination Delivery

            Supported.

         Prevention of Non-delivery Notification

            Not Supported, as there is no control in the RFC 822 world
            (but see Non-delivery Notification).

         Return of Contents

            This is normally the case, although the user has no control
            (but see Non-delivery Notification).

         Conversion Prohibition

            Supported.  Note that in practice this support is restricted
            by the nature of the gateway.

         Explicit Conversion

            Supported, for appropriate values (See the IPMS Typed Body
            service element).

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Implicit Conversion

            Supported, in the sense that there will be implicit
            conversion to IA5 in cases where this is practical.

         Probe

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

         Alternate Recipient Assignment

            N/A.

         Hold for Delivery

            N/A.

      2.2.2.  Interpersonal Message Service Elements

         IP-message Identification

            Supported.

         Typed Body

            Supported.  IA5 is fully supported.  ForwardedIPMessage is
            supported, with some loss of information.  A subset of TTX
            is supported (see section 5 for the specification of this
            subset), with some loss of information.  SFD may be
            supported, with some loss of information.  TTX and SFD are
            only supported when conversion is allowed.  Other types are
            not supported.

         Blind Copy Recipient Indication

            Supported.

         Non-receipt Notification

            Not supported.

         Receipt Notification

            Not supported.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Auto-forwarded Indication

            Supported as new RFC 822 header.

         Originator Indication

            Supported.

         Authorising User's Indication

            Supported, although the mapping (From:) is not quite the
            same.

         Primary and Copy Recipients Indication

            Supported.

         Expiry Date Indication

            Supported as new RFC 822 header.  In general, only human
            action can be expected.

         Cross Referencing Indication

            Supported.

         Importance Indication

            Supported as new RFC 822 header.

         Obsoleting Indication

            Supported as new RFC 822 header.

         Sensitivity Indication

            Supported as new RFC 822 header.

         Subject Indication

            Supported.

         Reply Request Indication

            Supported as comment next to address.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Forwarded IP-message Indication

            Supported, with some loss of information.

         Body Part Encryption Indication

            Not supported.

         Multi-part Body

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

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Chapter 3 -- Basic Mappings

   3.1.  Notation

      The P1 and P2 protocols are encoded in a structured manner
      according to the X.409 specifications, whereas RFC 822 is text
      encoded.  To define a detailed mapping, it is necessary to refer
      to detailed protocol elements in each format.  This is described.

      3.1.4.  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 "882." 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-P1 components).  In this case, the lexical analysis
                 defined in section 3 of RFC 822 should 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.bilateral-info).

            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.

      3.1.5.  X.409

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

            element        = protocol "." definition *( "." definition )
            protocol       = "P1" / "P2"
            definition     = identifier / context
            identifier     = ALPHA *< ALPHA or DIGIT or "-" >
            context        = "[" 1*DIGIT "]"

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         For example, P2.Heading.subject defines the subject element of
         the P2 heading.  The same syntax is also used to refer to
         element values. For example,
         P1.EncodedInformationTypes.[0].g3Fax refers to a value of
         P1.EncodedInformationTypes.[0] .

   3.2.  ASCII and IA5

      A gateway will interpret all IA5 as ASCII.  Thus, they are treated
      identically for the rest of this document.

   3.3.  Universal Primitives

      There is a need to convert between ASCII text, and some of the
      Universal Primitive types defined in X.409 [CCITT84d].  For each
      case, an EBNF syntax definition is given, for use in all of this
      specification.  All EBNF syntax definitions of Universal
      Primitives are in lower case, whereas X.409 primitives 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-delim )

            ps-char          = 1DIGIT /  1ALPHA / " " / "'" / "+" / ")"
                               / "," / "-" / "." / "/" / ":" / "=" / "?"

            ps-delim         = "("

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

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            ps-encoded       = *( ps-char / ps-encoded-char )

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

         The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127
         (Decimal), and is interpreted in decimal as the corresponding
         ASCII character. Special encodings are given for: at sign (@),
         percent (%), exclamation mark/bang (!), double quote ("), and
         underscore (_).  These characters 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.

         An asymmetric mapping between PrintableString and ASCII can now
         be defined <3>.  To encode ASCII as PrintableString, the
         EBNF.ps-encoded syntax is used, with all EBNF.ps-char AND
         EBNF.ps-delim mapped directly <4>.  All other 822.CHAR are
         encoded as EBNF.ps-encoded-char. There are two cases of
         encoding PrintableString as ASCII.  If the PrintableString can
         be parsed as EBNF.ps-encoded, then the previous mapping should
         be reversed.  If not, it should be interpreted as
         EBNF.printablestring.

         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)               <-    (a)
            (040)a(041)       ->    (a)
            (040)(a)          ->    (@
            ((a)              <-    (@

         The algorithm is designed so that it is simple to use in all
         common cases, so that it is general, and so that it is
         straightforward to code.  It is not attempting to minimise the
         number of pathological cases.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      3.3.4.  T.61String

         T.61 strings are, in general, only used for conveying human
         interpreted information.  Thus, the aim of a mapping should be
         to render the characters appropriately in the remote character
         set, rather than to maximise reversibility.  The mappings
         defined in the CEN/CENELEC X.400 functional standard should be
         used [CEN/CENELEC/85a].  These are based on the mappings of
         X.408 (sections 4.2.2 and 5.2.2).

      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 <5>.
         The UTCTime format which specifies the timezone offset should
         be used, in line with CEN/CENELEC recommendations.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

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 standard textual representation of
   X.400 addresses.

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

      822-address     = [ route ] addr-spec

   In an 822-P1 protocol, the originator and each recipient should be
   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 address is defined by P1.ORName.  In P1 all recipient
   P1.ORnames are encapsulated within P1.RecipientInfo, and in P2 all
   P2.ORNames <6> are encapsulated within P2.ORDescriptor.

   It can be seen that RFC 822 822.address must be mapped with
   P2.ORDescriptor, and that RFC 822 EBNF.822-address must be mapped
   with P1.ORName (originator) and P1.RecipientInfo (recipients).

   This chapter is structured as follows:

      4.1  Introduction.

      4.2  A textual representation of P1.ORName.  This is needed for
           the later mappings, and as a side effect provides a standard
           representation for O/R names.

      4.3  Mapping between EBNF.822-address and P1.ORName

      4.4  The Full P1 / 822-P1 Mapping

      4.5  The Full P2 / RFC 822 Mapping

      4.6  Mapping Message-IDs.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   4.1.  A textual representation of P1.ORName.

      P1.ORName is structured as a set of attribute value pairs.  It is
      clearly necessary to be able to encode this in ASCII for
      gatewaying purposes.  A general encoding is given here, which may
      be used as a basis for a user interface, as well as for the
      defined gateway mapping.

      4.1.1.  Basic Representation

         A series of BNF definitions of each possible attribute value
         pair is given, which is given a 1:1 mapping with the X.400
         encoding.  The rest of the mapping then talks in terms of these
         BNF components, with the mapping to X.400 encoding being
         trivial.

         attributevalue = c / admd / prmd / x121 / t-id / o / ou
                         / ua-id / pn.g / pn.i / pn.s / pn.gq / dd.value

         c        = printablestring       ; P1.CountryName
         admd     = printablestring       ; P1.AdministrationDomainName
         prmd     = printablestring       ; P1.PrivateDomainName
         x121     = numericstring         ; P1.X121Address
         t-id     = numericstring         ; P1.TerminalID
         o        = printablestring       ; P1.OrganisationName
         ou       = printablestring       ; P1.OrganisationalUnit
         ua-id    = numericstring         ; P1.UniqueUAIdentifier
         pn.s     = printablestring       ; P1.PersonalName.surName
         pn.g     = printablestring       ; P1.PersonalName.givenName
         pn.i     = printablestring       ; P1.PersonalName.initials
         pn.gq    = printablestring       ; P1.PersonalName.generation
                                            Qualifier
         dd.value = printablestring       ; P1.DomainDefined
                                            Attribute.value

         In cases where an attribute can be encoded as either a
         PrintableString or NumericString (Country, ADMD, PRMD) it is
         assumed that the NumericString encoding will be adopted if
         possible.  This prevents the encoding of PrintableString where
         the characters are all numbers. This restriction seems
         preferable to the added complexity of a general solution.
         Similarly, we can define a set of attribute types.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         dd.type = printablestring      ; P1.DomainDefinedAttribute.type

         standard-type =
                   "C"           ; P1.CountryName
                 / "ADMD"        ; P1.AdministrationDomainName
                 / "PRMD"        ; P1.PrivateDomainName
                 / "X121"        ; P1.X121Address
                 / "T-ID"        ; P1.TerminalID
                 / "O"           ; P1.OrganisationName
                 / "OU"          ; P1.OrganisationalUnit
                 / "UA-ID"       ; P1.UniqueUAIdentifier
                 / "S"           ; P1.PersonalName.surName
                 / "G"           ; P1.PersonalName.givenName
                 / "I"           ; P1.PersonalName.initials
                 / "GQ"          ; P1.PersonalName.generationQualifier

         standard-dd-type =
                   "RFC-822"     ; dd.type = "RFC-822"
                 / "JNT-Mail"    ; dd.type = "JNT-Mail"
                 / "UUCP"        ; dd.type = "UUCP"

      4.1.2.  Encoding of Personal Name

         Handling of 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 proposed here.  It is
         designed to cope with the common cases of O/R Name
         specification where:

            1.   There is no generational qualifier

            2.   Initials contain only letters <7>.

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

            4.   If Surname contains full stop, then it may not be in
                 the first two characters, and either initials or given
                 name is present.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         The following EBNF is defined:

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

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

            initial         = ALPHA

            surname         = printablestring

         Subject to the above restriction, this is a reversible mapping.

         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 CCITT guidelines suggest that Initials is used to
         encode ALL initials.  Therefore, the proposed 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!

      4.1.3.  Two encodings of P1.ORName

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

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            std-orname      = 1*( "/" attribute "=" value ) "/"
            attribute       = standard-type
                            / "PN"
                            / standard-dd-type
                            / registered-dd-type
                            / "DD." std-printablestring
            value           = std-printablestring
            registered-dd-type
                            = std-printablestring
            std-printablestring =
                            = *( std-char / std-pair )
            std-char        = <ps-delim, and any ps-char except "/"
                              and "=">
            std-pair        = "$" ( ps-delim / ps-char )

         If the type is PN, the value is interpreted according to
         EBNF.encoded-pn, and the components of P1.PersonalName derived
         accordingly.  If the value is registered-dd-type, if the value
         is registered at the SRI NIC as an accepted Domain Defined
         Attribute type, then the value should be interpreted
         accordingly.  This restriction maximises the syntax checking
         which can be done at a gateway.

         Another syntax is now defined.  This is intended to be
         compatible with the syntax used for 822.domains.  This syntax
         is not intended to be handled by users.

            dmn-orname      = dmn-part *( "." dmn-part )
            dmn-part        = attribute "$" value
            attribute       = standard-type
                            / "~" dmn-printablestring
            value           = dmn-printablestring
            dmn-printablestring =
                            = *( dmn-char / dmn-pair )
            dmn-char        = <ps-delim, and any ps-char except ".">
            dmn-pair        = "\."

         For example: C$US.ADMD$ATT.~ROLE$Big\.Chief

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   4.2.  Mapping between EBNF.822-address and P1.ORName

      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.

      4.2.1.  X.400 encoded in RFC 822

         The std-orname syntax is  used to encode O/R Name information
         in the 822.local-part of EBNF.822-address.  Further  O/R Name
         information may be associated with the 822.domain component.
         This cannot be used in the general case, basically due to
         character set problems, and lack of order in X.400 O/R Names.
         The only way to encode the full PrintableString character set
         in a domain is by use of the 822.domain-ref syntax.  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.

         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)
         should be 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 may
         also identify the gateway from within the RFC 822 world.  This
         final 822.domain may be used to determine some number of O/R
         Name attributes.  The following O/R Name 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

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         There may be multiple Organisational Units.

         Associations may be defined between domain specifications, and
         some set of attributes.  This association proceeds
         hierarchically: i.e. if a domain implies ADMD, it also implies
         country.  If one of the hierarchical components is omitted from
         an X.400 structure, this information can be associated with the
         corresponding domain (e.g. a domain can be mapped onto a
         Country/ADMD/Organisation tuple). Subdomains under this are
         associated according to the O/R Name hierarchy.  For example:

            => "AC.UK" might be associated with
                                          C="234", ADMD="BT", PRMD="DES"

            then domain "R-D.Salford.AC.UK" maps with
                   C="234", ADMD="BT", PRMD="DES", O="Salford", OU="R-D"

         There are two 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   = ALPHA [ *alphanumhyphen alphanum ]
               alphanum        = <ALPHA or DIGIT>
               alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>

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

         This provides a general aliasing mechanism.

         This set of mappings need only be known by the gateways
         relaying between the RFC 822 world, and the O/R Name namespace
         associated with the mapping in question.  However, it is
         desirable (for the optimal mapping of third party addresses)
         for all gateways to know these mappings.  A format for the
         exchange of this information is defined in Appendix F.

         From the standpoint of the RFC 822 Message Transfer System, the
         domain specification is simply used to route the message in the

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         standard manner.  The standard domain mechanisms are used to
         identify gateways, and are used to select appropriate gateways
         for the corresponding O/R Name namespace.  In most cases, this
         will be done by registering the higher levels, and assuming
         that the gateway can handle the lower levels.

         As a further mechanism to simplify the encoding of common
         cases, where the only attributes to be encoded on the LHS are
         Personal Name attributes which comply with the restrictions of
         4.2.2, the 822.local-part may be encoded as EBNF.encoded-pn.

         An example encoding is:

            /PN=J.Linnimouth/GQ=5/@Marketing.Xerox.COM

            encodes the P1.ORName consisting of

               P1.CountryName                  = "US"
               P1.AdministrationDomainName     = "ATT"
               P1.OrganisationName             = "Xerox"
               P1.OrganisationalUnit           = "Marketing"
               P1.PersonalName.surName         = "Linnimouth"
               P1.PersonalName.initials        = "J"
               P1.PersonalName.GenerationQualifier = "5"

            If the GenerationQualifier was not present, the encoding
            J.Linnimouth@Marketing.Xerox.COM could be used.

         Note that in this example, the first three attributes are
         determined by the domain Xerox.COM.  The OrganisationalUnit is
         determined systematically.

         There has been an implicit assumption that an RFC 822 domain is
         either X.400 or RFC 822.  This is pragmatic, but undesirable,
         as the namespace should be structured on a logical basis which
         does not necessarily correspond to the choice of Message
         Transfer protocols. The restriction can be lifted, provided
         that the nameservice deals with multiple message transfer
         protocols.  This can happen in a straightforward manner for the
         UK NRS, as explained in [Kille86a].  It could also be achieved
         with the DARPA Domain Nameserver scheme by use of the WKS
         mechanism.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      4.2.2.  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.
         Three are defined, according to the full environment used to
         interpret the RFC 822 information.

            1.   Domain defined type "RFC-822".  This string is to be
                 interpreted in the context of RFC 822, and RFC 920
                 [Crocker82a,Postel84a].

            2.   Domain defined type "JNT-Mail".  This string is to be
                 interpreted in the context of the JNT Mail protocol,
                 and the NRS [Kille84a,Larmouth83a].

            3.   Domain defined type "UUCP".  This is interpreted
                 according to the constraints of the UUCP world
                 [Horton86a].

         These three are values currently known to be of use.  Further
         recognised values may be defined.  These will be maintained in
         a list at the SRI Network Information Center.

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

            1)

            C               = "GB"
            ADMD            = "BT"
            PRMD            = "AC"
            "JNT-Mail"      = "Jimmy(a)UK.CO.BT-RESEARCH-LABS"

            2)

            C               = "US"
            ADMD            = "Telemail"
            PRMD            = "San Fransisco"
            O               = "U Cal"
            OU              = "Berkeley"
            "RFC-822"       = "postel(a)usc-isib.arpa"

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Note in each case the PrintableString encoding of "@" as "(a)".
         In the first example, the "JNT-Mail" domain defined attribute
         is interpreted everywhere within the (Administrative or
         Private) Management Domain.  In the second 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.

      4.2.3.  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 should proceed as follows, by first assuming case
         1).

         STAGE 1.

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

               local-part "@" domain

               go to stage 2.

            2.   Attempt to parse domain as:

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

               Where known-domain is the longest possible match in a
               list of gatewayed domains.  If this fails, and the domain
               does not explicitly identify the local gateway, go to
               stage 2.  If it succeeds, allocate the attributes
               associated with EBNF.known-domain, and systematically
               allocate the attributes implied by each
               EBNF.domain-syntax component.

            3.   Map 822.local-part to ASCII, according to the
                 definition of Appendix A.  This step should be applied:

               A.  If the source network cannot support
                   822.quoted-string (as discussed in Appendix A).

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

               B.  If the address is an 822-P1 recipient.

                  This mapping is always applied in case B, as it
                  increases the functionality of the gateway, and does
                  not imply any loss of generality.  Mapping case B
                  allows sites which cannot generate 822.quoted-string
                  to address recipients the gateway, without the gateway
                  having to know this explicitly.  There is no loss of
                  functionality, as the quoting character of Appendix A
                  (#) is not in PrintableString.  This seems desirable.
                  It should not be applied in to other addresses, as a
                  third party RFC#822 address containing the sequence
                  EBNF.atom-encoded (as defined in Appendix A) would be
                  transformed asymmetrically.

            4.   Map the result of 3) to EBNF.ps-encoded according to
                 section 3.

            5.   Parse the result of 4) according to the EBNF
                 EBNF.std-orname.  If this parse fails, parse the result
                 of 4) according to the EBNF EBNF.encoded-pn.  If this
                 also fails, go to stage 2.  Otherwise, the result is a
                 set of type/value pairs.

            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 2.

            7.   Ensure that the set of attributes conforms both to the
                 X.411 P1.ORName specification and to the restrictions
                 on this set given in X.400.  If not go to stage 2.

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

         STAGE 2.

         This will only be reached if the RFC 822 EBNF.822-address is
         not a valid X.400 encoding.  If the address is an 822-P1
         recipient address, it must be rejected, as there is a need to
         interpret such an address in X.400.  For the 822-P1 return
         address, and any addresses in the RFC 822 header, they should
         now be encoded as RFC 822 addresses in an X.400 O/R Name:

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

            2.   The domain defined attribute ("RFC-822", "JNT-Mail" or

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

                 "UUCP") appropriate to the gateway should be selected,
                 and its value set.

            3.   Build the rest of the O/R Name in the local Management
                 Domain agreed manner, so that the O/R Name will receive
                 a correct global interpretation.

      4.2.4.  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 P1 Recipient O/R Name is interpreted, gatewaying will be
         selected if there a single special domain defined attribute
         present ("RFC-822", "JNT-Mail" or "UUCP").  In this case, use
         mapping A.  For other O/R Names which

            1.   Contain the special attribute.

               AND

            2.   Identify the local gateway with the other attributes.

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

         Mapping A

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

            2.   Where appropriate (P1 recipients), interpret the string
                 according to the semantics implied by the domain
                 defined attribute.

         Mapping B.

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

            1.   Noting the hierarchy specified in 4.3.1, determine the
                 maximum set of attributes which have an associated
                 domain specification. If no match is found, allocate

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

                 the domain as the domain specification of the local
                 gateway, and go to step 4.

            2.   Following the 4.3.1 hierarchy, if each successive
                 component exists, and conforms to the syntax
                 EBNF.domain-syntax (as defined in 4.3.1), allocate the
                 next subdomain.

            3.   If the remaining components are personal-name
                 components, conforming to the restrictions of 4.2.2,
                 then EBNF.encoded-pn should be derived to form
                 822.local-part.  In other cases the remaining
                 components should simply be encoded as a 822.local-part
                 using the EBNF.std-orname syntax.  Where registered
                 domain defined types exist, the DD. syntax should not
                 be used.

            4.   If this step is reached for an 822-P1 recipient, then
                 the address is invalid.  For other addresses, if the
                 derived 822.local-part can only be encoded by use of
                 822.quoted-string, the gateway may optionally use the
                 ASCII to 822.local-part mapping defined in Appendix A,
                 dependent on the mail protocols of the networks being
                 relayed to.  Use of this encoding is discouraged.

   4.3.  Repeated Mappings

      The mappings defined are symmetrical across a single gateway,
      except in certain pathological cases (see chapter 3).  However, it
      is always possible to specify any valid address across a gateway.
      This 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 names 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.

      However, the syntax may be used to source route.

      For example:  X.400 -> RFC 822  -> X.400

         C               = "UK"
         ADMD            = "BT"
         PRMD            = "AC"
         "JNT-Mail"      = "/PN=Duval/DD.Title=Manager/(a)FR.PTT.Inria"

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         This will be sent to an arbitrary UK Academic Community gateway
         by X.400.  Then by JNT Mail to another gateway determined by
         the domain FR.PTT.Inria.  This will then derive the X.400 O/R
         Name:

            C               = "FR"
            ADMD            = "PTT"
            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

         /C=UK/ADMD=BT/PRMD=AC/RFC-822=jj#l#a#r#seismo.css.gov/
                                                     @monet.berkeley.edu

         The second case uses the Appendix A encoding to avoid
         822.quoted-text. 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.

   4.4.  The full P1 / 822-P1 mapping

      There are two basic mappings at the P1 level:

         1.   822-P1 return address <-> P1.UMPDUEnvelope.originator

         2.   822-P1 recipient <-> P1.RecipientInfo

      822-P1 recipients and return addresses are encoded as
      EBNF.822-address.  As P1.UMPDUEnvelope.originator is encoded as
      P1.ORName, mapping 1) has already been specified.
      P1.RecipientInfo contains a P1.ORName and additional information.
      The handling of this additional information is now specified.

      4.4.1.  RFC 822 -> X.400

         The following default settings should be made for each
         component of P1.RecipientInfo.

            P1.ExtensionIdentifier

               This can be set systematically by the X.400 system.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P1.RecipientInfo.perRecipientFlag

               Responsibility Flag should be set.  Report Request should
               be set according to content return policy, as discussed
               in section 5.3. User Report Request should be set to
               Basic.

            P1.ExplicitConversion

               This optional component should be omitted.

      4.4.2.  X.400 -> RFC 822

         The mapping only takes place in cases where
         P1.RecipientInfo.perRecipientFlag Responsibility Flag is set.
         The following treatment should be given to the other
         P1.RecipientInfo components.

            P1.ExtensionIdentifier

               Not used.

            P1.RecipientInfo.perRecipientFlag

               If ReportRequest is Confirmed or Audit-and-Confirmed then
               a delivery report indicating success should be sent by
               the gateway. This report should use each
               P1.ReportedRecipientInfo.SupplementaryInformation to
               indicate the identity of the gateway, and the nature of
               the report (i.e. only as far as the gateway).  Failures
               will be handled by returning RFC 822 messages, and so
               User Report Request set to No report is ignored.

            P1.ExplicitConversion

               If present, the O/R name should be rejected, unless the
               requested conversion can be achieved.  None of the
               currently recognised values of this parameter are
               appropriate to a gateway using this specification.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   4.5.  The full P2 / RFC 822 mapping

      All RFC 822 addresses are assumed to use the 822.mailbox syntax.
      This should include all 822.comments associated with the lexical
      tokens of the 822.mailbox.  All P2.ORNames are encoded within the
      syntax P2.ORDescriptor, or P2.Recipient (or within Message IDs).
      An asymmetrical mapping is defined between these components.

      4.5.1.  RFC 822 -> X.400

         The following sequence is followed.

            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 P2.ORName as described above.

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

               -    The 822.phrase component if it is a 822.phrase
                    822.route-addr construct.

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

                  This string should then be encoded into T.61 (as
                  described in chapter 3).  If the string is not null,
                  it should be assigned to P2.ORDescriptor.freeformName.

            3.   P2.ORDescriptor.telephoneNumber should be omitted.

            4.   In cases of converting to P2.Recipient,
                 P2.Recipient.replyRequest and
                 P2.Recipient.reportRequest should be omitted.

         If the 822.group construct is present, each included
         822.mailbox should be encoded as above.  The 822.group should
         be mapped to T.61, and a P2.ORDesciptor with only a
         freeformName component built from it.

      4.5.2.  X.400 -> RFC 822

         In the basic case, where P2.ORName is present, proceed as
         follows.

            1.   Encode P2.ORName as EBNF.822-address.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            2a.  If P2.ORDescriptor.freeformName is present, convert it
                 to ASCII (chapter 3), and use use this as the
                 822.phrase component of 822.mailbox using the
                 822.phrase 822.route-addr construct.

            2b.  If P2.ORDescriptor.freeformName 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 should be added.

            3.   If P2.ORDescriptor.telephoneNumber is present, this
                 should be placed in a trailing 822.comment.

            4.   If P2.Recipient.reportRequest has the
                 receiptNotification bit set, then an 822.comment
                 "(Receipt Notification Requested)" should be appended
                 to the address.  The effort of correlating P1 and P2
                 information is too great to justify the gateway sending
                 Receipt Notifications.

            5.   If P2.Recipient.replyRequest is present, an 822.comment
                 "(Reply requested)" or "(Reply not requested)" should
                 be appended to the address, dependent on its value.

         If P2.ORName is absent, P2.ORDescriptor.freeformName should be
         converted to ASCII, and used with the RFC 822 822.group syntax:

            freeformname ":" ";"

         Steps 3-5 should then be followed.

   4.6.  Message IDs

      There is a need to map both ways between 822.msg-id and
      P2.IPMessageID.  A mapping is defined which is symmetrical for
      non-pathological cases.  The mapping allows for the fact that
      P2.IPMessageID.PrintableString is mandatory for the Cen/Cenelec
      profile.  This allows for good things to happen when messages pass
      multiple times across the X.400/RFC 822 boundary.  A mapping
      between 822.msg-id and P1.MPDUIdentifier is defined.  This allows
      for X.400 error messages to reference an RFC 822 ID, which is
      preferable to a gateway generated ID.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      4.6.1.  P2.IPMessageID -> 822.msg-id

         P2.IPMessageID.ORName is used to generate an 822.addr-spec, as
         defined above.  P2.IPMessageID.PrintableString is mapped to
         ASCII, as defined in chapter 3.  This string (if it is present
         and if the value is not "RFC-822") is appended to the front of
         the 822.local-part of the 822.msg-id, with "*" as a separator.
         If no ORName is present, an 822.msg-id of the form
         "PrintableString*@gateway-domain" is generated.

      4.6.2.  822.msg-id -> P2.IPMessageID

         822.local-part is parsed as:

            [ printablestring "*" ] real-local-part

         If EBNF.printablestring is found, it is mapped to
         PrintableString, and used as P2.IPMessageID.PrintableString.
         Otherwise
         P2.IPMessageID.PrintableString is set to "RFC-822".  This
         arbitrary value allows for conformance to Cen/Cenelec.  If
         EBNF.real-local-part is not present, no P2.IPMessageID.ORName
         is generated.  Otherwise,  822.local-part is replaced with
         EBNF.real-local-part, and 822.addr-spec is mapped to
         P2.IPMessageID.ORName as defined above.

      4.6.3.  822.msg-id -> P1.MPDUIdentifier

         P1.CountryName is assigned to "", P1.AdministrationDomainName
         to 822.domain (from 822.msg-id) and P1.MPDUIdentifier.IA5String
         to 822.local-part (from 822.msg-id).

      4.6.4.  P1.MPDUIdentifier -> 822.msg-id

         822.local-part is set to P1.MPDUIdentifier.IA5String, with any
         CRLF mapped to SPACE.  If P1.CountryName is "", 822.domain is
         set to P1.AdministrationDomainName; Otherwise to
         P1.AdministrationDomainName ".." P1.CountryName.  If there are
         any specials,  the domain literal encoding should be used.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Chapter 5 -- Protocol Elements

   This chapter gives 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.  This chapter is structured as
   follows:

      5.1. Basic RFC 822 -> X.400 mappings

      5.2. A definition of some new RFC 822 elements, and their mapping
           to X.400.

      5.3  Some special handling associated with Return of Contents.

      5.4. X.400 -> RFC 822

   5.1.  RFC 822 -> X.400

      First, the basic functions of an 822-P1 protocol should be mapped
      as follows:

         822-P1 Originator

            Mapped to P1.UMPDUEnvelope.originator (see chapter 4).

         822-P1 Recipient

            Mapped to P1.RecipientInfo (see chapter 4).

      The RFC 822 headers are used to generate both a P1.UMPDUEnvelope
      and a P2.Heading.  The IP Message will have either one or two
      P2.BodyParts which will be type P2.IA5Text with no
      P2.IA5Text.repertoire component. The last P2.BodyPart will contain
      the RFC 822 message body.  If there are any RFC 822 headers which
      indicate mapping into the P2.BodyPart, then two P2.BodyParts are
      generated.  If a revised version of P2 allowed for extensible
      header specification, this would be seen as a preferable mapping.
      The first body part will start with the line:

         RFC-822-Headers:

      The rest of this body part will contain all of the headers not
      otherwise mapped (both 822.field-name and 822.field-body).  The
      order of any such headers should be preserved.  Similarly,
      ordering within P2.Heading and P1.UMPDUEnvelope should reflect
      ordering within the RFC 822 header.  No P1 or P2 optional fields
      are generated unless specified.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      A pro-forma X.400 message is now specified.  Some of these
      defaults may be changed by the values in the RFC 822 message being
      mapped.  The mandatory P1 and P2 components have the following
      defaults.

         P1.MPDUIdentifier

            The default should be unique value generated by the gateway.

         P1.OriginatorORName

            Always generated from 822-P1.

         P1.ContentType

            P1.ContentType.p2

         P1.RecipientInfo

            These will always be supplied from 822-P1.

         P1.Trace

            The last P1.TraceInformation component is generated such
            that: P1.TraceInformation.GlobalDomainIdentifier is set to
            the local vaglue.  P1.DomainSuppliedInfo.action is set to
            relayed. P1.DomainSuppliedInfo.arrival is set to the current
            time. P1.DomainSuppliedInfo.previous may be set if there is
            anything sensible to set it to.

         P2.IPMessageID

            The default should be a unique value generated by the
            gateway.

      The following optional parameters should be set:

         P1.PerMessageFlag

            The P1.PerMessageFlag.contentReturnRequest bit should be set
            according to the discussion in section 5.3.  The
            P1.PerMessageFlag.alternateRecipientAllowed bit should be
            set, as it seems desirable to maximise opportunity for
            (reliable) delivery.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      The RFC 822 headings should be mapped as follows:

         Received:

            Fudged onto P1.TraceInformation (try not to grimace too
            much). P1.DomainSuppliedInfo.action is set to relayed.
            P1.DomainSuppliedInfo.arrival is set to the date-time
            component P1.TraceInformation.GlobalDomainIdentifier has
            P1.CountryName as a null string, and
            P1..AdministrationDomainName as the domain of the receiving
            host (if present - null string if not).
            P1.DomainSuppliedInfo.previous has P1.CountryName as a null
            string, and P1.AdministrationDomainName has the domain of
            the sending host with all other information enclosed in
            round parentheses.  The encoding of ASCII to PrintableString
            (chapter 3) should be used if needed.  For example:

               Received: from 44e.cs.ucl.ac.uk by vax2.Cs.Ucl.AC.UK
                              with SMTP  id a002110; 18 Dec 85 10:40 GMT

                  maps to -

                  P1.GlobalDomainIdentifier
                     CountryName                  = ""
                     AdministrationDomainName     = "vax2.Cs.Ucl.AC.UK"
                  P1.DomainSuppliedInfo
                     arrival                      = 18 Dec 85 10:40 GMT
                     action                       = relayed
                     previous
                        CountryName               = ""
                        AdministrationDomainName  =
                               "44e.cs.ucl.ac.uk (with SMTP id a002110)"

         Date:

            This is used to set the first component of
            P1.TraceInformation. The mandatory components are set as
            follows:

               P1.GlobalDomainIdentifier
                  CountryName                  = ""
                  AdministrationDomainName     = ""
               P1.DomainSuppliedInfo
                  arrival                      = time derived from Date:
                  action                       = relayed

            No optional fields are used in the trace.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Message-Id:

            Mapped to P2.IPMessageID.  If the RFC 822 message does not
            contain a P1-Message-ID: field, the Message-Id: field is
            also mapped to P1.MPDUIdentifier.  For these, and all other
            fields containing msg-id the mappings of chapter 4 are used
            for each msg-id.

         From:

            If Sender: is present, this is mapped to
            P2.AuthorisingUsers.  If not, it is mapped to P2.Originator.
            For this, and other components containing addresses, the
            mappings of chapter 4 are used for each address.

         Sender:

            Mapped to P2.Originator.

         Reply-To:

            Mapped to P2.Heading.replyToUsers.

         To:

            Mapped to P2.Heading.primaryRecipients

         Cc:

            Mapped to P2.Heading.copyRecipients.

         Bcc:

            Mapped to P2.Heading.blindCopyRecipients.

         In-Reply-To:

            Mapped to P2.Heading.inReplyTo for the first (if any)
            822.msg-id component.  If the field contains an 822.phrase
            component, or there are multiple 822.msg-id components, the
            ENTIRE field is passed in the P2.BodyPart.

         References:

            Mapped to P2.Heading.crossReferences.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         Keywords:

            Passed in the P2.BodyPart.

         Subject:

            Mapped to P2.Heading.subject.  The field-body uses the
            mapping referenced in chapter 3 from ASCII to T.61.

         Comments:

            Passed in the P2.BodyPart.

         Encrypted:

            Passed in the P2.BodyPart.

         Resent-*

            Passed in the P2..BodyPart <8>.

         Other Fields

            In particular X-* fields, and "illegal" fields in common
            usage (e.g. "Fruit-of-the-day:") are passed in the
            P2.BodyPart.  The same treatment should be applied to
            RFC 822 fields where the content of the field does not
            conform to RFC 822 (e.g. a Date: field with unparsable
            syntax).

   5.2.  Extended RFC 822 Elements -> X.400

      First an EBNF definition of a number of extended fields is given,
      and then a mapping to X.400 is defined.  In most cases, the
      RFC 822 syntax is defined to make this mapping very
      straightforward, and so no detailed explanation of the mapping is
      needed.

         extended-field  = "P1-Message-ID" ":" p1-msg-id
                         / "X400-Trace" ":" x400-trace
                         / "Original-Encoded-Information-Types"
                            ":"encoded-info
                         / "P1-Content-Type" ":" p1-content-type
                         / "UA-Content-ID" ":" printablestring
                         / "Priority" ":" priority
                         / "P1-Recipient" : 1 mailbox
                         / "Deferred-Delivery" ":" date-time

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

                         / "Bilateral-Info" ":" bilateral-info
                         / "Obsoletes" ":" 1 msg-id
                         / "Expiry-Date" ":" date-time
                         / "Reply-By" ":" date-time
                         / "Importance" ":" importance
                         / "Sensitivity" ":" sensitivity
                         / "Autoforwarded" ":" boolean

         p1-msg-id       = global-id ";" *text

         p1-content-type = "P2" / atom

         x400-trace      = global-id ";"
                         "arrival" date-time
                         [ "deferred" date-time ]
                         [ "action" action ]
                         [ "converted" "(" encoded-info ")" ]
                         [ "previous" global-id ]

         action          = "Relayed" / "Rerouted" / escape

         global-id       = c "*" admd [ "*" prmd ]

         encoded-info    = 1 encoded-type

         encoded-type    = "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)
                         / escape

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

         bilateral-info  = c "*" admd "*" *text

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

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

         escape          = 1*DIGIT

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      With the exception of "Bilateral-Info:" and "X400-Trace:", there
      must be no more than one of each of these fields in an RFC 822
      header.  Any field beginning with the String "Autoforwarded-" is
      valid if the field would be syntactically valid with this string
      removed.

      The mappings to X.400 are as follows:

         P1-Message-ID:

            Mapped to P1.UMPDUEnvelope.MPDUIdentifier.  This take
            precedence over any value derived from Message-ID:.

         X400-Trace:

            Mapped to the next component of
            P1.UMPDUEnvelope.Traceinformation.  Care should be taken to
            preserve order.  If one or more of these mappings is made,
            then a trace component should NOT be generated from the
            Date: field which should be redundant.  This is because the
            message has previously come from X.400, and the Date:
            information will be redundant.  Note that all trace
            information (Received: and "X400-Trace:") in the RFC 822
            message will be in strict order, with the most recent at the
            top.  This order should be preserved in the mapping.

         Original-Encoded-Information-Types:

            This is used to set P1.UMPDUEnvelope.original.
            P1.EncodedInformationTypes.[0] has bits set according to
            each of the encoded-info components in this field.  Any
            escape values should not be encoded.

         P1-Content-Type:

            If the value is anything other than "P2", the mapping should
            not be performed (unless the new value has some semantics to
            the gateway).

         UA-Content-ID:

            Mapped to P1.UMPDUEnvelope.UAContentID.

         Priority:

            Mapped to P1.UMPDUEnvelope.Priority.  An escape value should
            be encoded as P1.Priority.normal.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         P1-Recipient:

            If this field is set, the
            P1.PerMessageFlag.discloseRecipients bit should be set.  Any
            of the addresses here which do not correspond to 822-P1
            recipients should be added to the P1 recipient list, with
            the responsibility bit turned off.

         Deferred-Delivery:

            Mapped to P1.UMPDUEnvelope.deferredDelivery.  Note that the
            value of this field should always be in the past, as this
            field should only be present in messages which have come
            originally from X.400.  Thus there should be no implied
            action.  See also the comments on the reverse mapping.

         Bilateral-Info:

            No attempt is made to reconvert this information back to
            X.400.

         Obsoletes:

            Mapped to P2.Heading.obsoletes.

         Expiry-Date:

            Mapped to P2.Heading.expiryDate.

         Reply-By:

            Mapped to P2.Heading.replyBy.

         Importance:

            Mapped to P2.Heading.importance.  An escape value should be
            encoded as P2.Heading.importance.normal.

         Sensitivity:

            Mapped to P2.Heading.sensitivity.  An escape value should be
            encoded as P2.Heading.sensitivity.normal.

         Autoforwarded:

            If this field is present and the value is "TRUE", there will
            be zero or more field names beginning "Autoforwarded-".

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            These should be taken, and the string "Autoforwarded-"
            stripped.  These fields, in conjunction with the 822-P1
            information should be used to build an IP Message.  Any
            implied actions should be taken. P2.Heading.autoforwarded is
            set in this message.  The other RFC 822 fields are used to
            build another IP Message, which is used as the single body
            part of the first message.  This mechanism does not nest.

   5.3.  Return of Contents

      It is not clear how widely supported X.400 return of contents
      service will be.  However, profiling work suggests that most
      systems will not support this service.  As this service is
      expected in the RFC 822 world, two approaches are specified (it is
      not so necessary in the X.400 world, as delivery reports are
      distinguished from messages).  The choice will depend on the
      service level of the X.400 community being serviced by the
      gateway.

      In environments where return of contents is widely supported, the
      P1.PerMessageFlag content return request bit will be set, and the
      Report Request bit in P1.PerRecipientFlag will be set to
      Confirmed, for every message passing from RFC 822 -> X.400.  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 provisions to handle return of
      contents.  For every message passing from RFC 822 -> X.400, the
      P1.PerMessageFlag content return request bit will be set, and the
      Report Request bit in P1.PerRecipientFlag will be set to
      Confirmed.  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-P1 originator.  If no report is received for a
      recipient, a (timeout) failure notice should be sent to the 822-P1
      originator.  The gateway may retransmit the X.400 message if it
      wishes.  Delivery confirmations should only be sent back to the
      822-P1 originator if the P1.PerRecipientFlag User Report Request
      bit is set to Confirmed.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   5.4.  X.400 -> RFC 822

      5.4.1.  General

         This section describes how to build a pro-forma message, and
         then explains how these defaults may be overridden.  It should
         be noted that RFC 822 folding of headers should be used in an
         appropriate manner.

      5.4.2.  Service MPDU

         5.4.2.1.  Probe

            Any P1.ProbeMPDU should 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 a
            User MPDU with the values specified in the probe.  The reply
            should make use of P1.SupplementaryInformation to indicate
            that the probe was serviced by the gateway.

         5.4.2.2.  Delivery Report

            The 822-P1 components are constructed as follows:

               822-P1 Originator

                  This is set to an 822.addr-spec pointing to an
                  administrator at the gateway.

               822-P1 Recipient

                  The single recipient is constructed from
                  P1.DeliveryReportEnvelope.originator, using the
                  mappings of chapter 4.

            The mandatory RFC 822 headers for an RFC 822 pro-forma are
            constructed as follows:

               Date:

                  From the P1.DomainSuppliedInfo.arrival component of
                  the first P1.TraceInformation component.

               From:

                  This is set to the same as the 822-P1 originator.  An

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

                  appropriate phrase component may be added (e.g. giving
                  the name of the gateway).

               To:

                  The same as the 822-P1 recipient.

            A Subject: field should be added, which contains some
            appropriate words (e.g. "Delivery Report").

            The other two P1.DeliveryReportEnvelope parameters should be
            mapped as follows:

               P1.DeliveryReportEnvelope.report

                  This should be mapped to a P1-Message-Id: field.

               P1.DeliveryReportEnvelope.TraceInformation

                  Each component should be mapped to an "X400-Trace:"
                  field.  RFC 822 and X.400 ordering should be
                  maintained (see 5.3).

            The P1.DeliveryReportContent parameters should be mapped to
            a series of new RFC 822 headers.  These new headers are
            intended for processing in the RFC 822 world.  No attempt
            will be made to reverse the mappings.

               drc-field    = "Delivery-Report-Content-Original"
                           ":" msg-id
                 / "Delivery-Report-Content-Intermediate-Trace"
                           ":" x400-trace
                 / "Delivery-Report-Content-UA-Content-ID"
                           ":" printablestring
                 / "Delivery-Report-Content-Billing-Information"
                           ":" *text
                 / "Delivery-Report-Content-Reported-Recipient-Info"
                           ":" drc-info

               drc-info     = mailbox ";"
                            last-trace ";"
                            "ext" 1*DIGIT
                            "flags" 2DIGIT
                            [ "intended" mailbox ] ";"
                            [ "info" printablestring ]

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

               last-trace   = drc-report ";"
                            date-time ";"
                            [ "converted" "(" encoded-info ")"

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

               drc-success  = date-time ";" 1*DIGIT

               drc-failure  = *text [ ";" *text ] ";"

            There may be multiple
            "Delivery-Report-Content-Intermediate-Trace:" and
            "Delivery-Report-Content-Reported-Recipient-Info:" fields.
            The msg-id for "Delivery-Report-Content-Original" is derived
            according to the mapping of chapter 4.  EBNF.drc-failure may
            use numeric values or textual explanation.  The latter is
            preferred.  All P1.DeliveryReportContent parameters are
            mapped to the corresponding component.  The order of
            "Delivery-Report-Content-Intermediate-Trace:" should have
            the most recently stamped one first.

            The body of the RFC 822 message should be a human readable
            description of the critical parts of the
            P1.DeliveryReportContent.  In particular, the failed
            recipients, and failure reason should be given.  Some or all
            of the original message should be included in the delivery
            report. The original message will be available at the
            gateway, as discussed in section 5.3.

      5.4.3.  User MPDU

         These elements are the basis for both Status Report and IP
         Message.

         The 822-P1 components are constructed as follows:

            822-P1 Originator

               This is derived from P1.UMPDUEnvelope.originator.

            822-P1 Recipient

               Each recipient is constructed from the P1.RecipientInfo,
               as described in chapter 4.  This describes actions as
               well as format mappings.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         The mandatory RFC 822 field pro-forma is derived as follows.
         In most cases where the P1.UMPDUContent is an IP Message, these
         defaults will be overridden:

            Date:

               From the P1.DomainSuppliedInfo.arrival component of the
               first P1.TraceInformation component.

            From:

               From the P1.UMPDUEnvelope.originator, as defined in
               chapter 4.

            To:

               This default is only required if the generated RFC 822
               message has no destination specification.  If
               P1.PerMessageFlag.discloseRecipients is set then it
               should contain the ORName in each P1.RecipientInfo
               component.  If it is not set, the it should be set to
               "To: No Recipients Specified : ;".

         The mappings, and any actions for each P1.UserMPDU element is
         now considered.

            P1.MPDUIdentifier

               Mapped to the extended RFC 822 field "P1-Message-ID:".
               Note that the sequence CRLF is mapped to SPACE, which
               makes the mapping irreversible for such cases.

            P1.UMPDUEnvelope.original

               Mapped to the extended RFC 822 field
               "Original-Encoded-Information-Types:".  If it contains
               only P2.IA5Text, the RFC 822 field may be omitted.

            P1.ContentType

               As this can currently only have one value, it is not
               mapped, on the basis that it is redundant.  If the field
               contains any value other than P2, then the UMPDU should
               be rejected.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P1.UAContentID

               Mapped to the extended RFC 822 field "UA-Content-Id:".

            P1.Priority

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

            P1.PerMesageFlag

               This has a number of components:

                  - discloseRecipients

                     If this bit is set, a "P1-Recipient:" field should
                     be generated, and contain each of the P1
                     recipients.

                  - conversionProhibited

                     If this bit is set, the message should be rejected
                     if it contains P2.BodyPart which is not P2.IA5Text
                     or P2.ForwardedIPMessage.

                  - alternateRecipientAllowed

                     The value of this bit is ignored.

                  - contentReturnRequest

                     The value of this bit is ignored.

            P1.UMPDUEnvelope.deferredDelivery

               This should be mapped to the extended RFC 822 field
               "Deferred-Delivery:".  X.400 profiles, and in particular
               the CEN/CENELEC profile [CEN/CENELEC/85a], specify that
               this element must be supported at the first MTA.  Thus,
               it is expected that the value of this element will always
               be in the past.  If it is not, the function may
               optionally be implemented by the gateway: that is, the
               gateway should hold the message until the time specified
               in the protocol element.  Thus the extended RFC 822 field
               is just for information.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P1.PerDomainBilateralInformation

               Each component should be encoded in the extended RFC 822
               field "Bilateral-Info:".  P1.BilateralInfo should be
               mapped into ASCII in a manner appropriate to its
               contents.  This submapping is not reversible.

            P1.TraceInformation

               This should be mapped to "X400-Trace:", as for the
               delivery report.

      5.4.4.  Status Report

         The entire status report is mapped into the body of the RFC 822
         message, in the same manner as for a Delivery Report.  An
         appropriate "Subject:" field should be generated.  As status
         reports cannot be requested from the RFC 822 world, the mapping
         is not likely to be used a great deal.

      5.4.5.  IP Message

         The P1.UMPDUEnvelope pro-forma specification ensures all the
         822-P1 information, and a minimal (legal) RFC 822 message.  The
         mappings and actions for the P2.Heading components are now
         described.  Basically, these are interpreted as actions and/or
         mappings into RFC 822 fields. The following mappings are
         specified:

            P2.IPMessageID

               This is mapped to the field "Message-ID:", according to
               section 4.

            P2.Heading.originator

               If P2.Heading.authorisingUsers is present this is mapped
               to Sender:, if not to From:.

            P2.Heading.authorisingUsers

               Mapped to From:.

            P2.Heading.primaryRecipients

               Mapped to To:.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P2.Heading.copyRecipients

               Mapped to Cc:.

            P2.Heading.blindCopyRecipients

               Mapped to Bcc:.

            P2.Heading.inReplyTo

               Mapped to In-Reply-To:.

            P2.Heading.obsoletes

               Mapped to the extended RFC 822 field "Obsoletes:"

            P2.Heading.crossReferences

               Mapped to References:.

            P2.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.  line.

            P2.Heading.expiryDate

               Mapped to the extended RFC 822 field "Expiry-Date:".

            P2.Heading.replyBy

               Mapped to the extended RFC 822 field "Reply-By:".

            P2.Heading.replyToUsers

               Mapped to Reply-To:.

            P2.Heading.importance

               Mapped to the extended RFC 822 field "Importance:".

            P2.Heading.sensitivity

               Mapped to the extended RFC 822 field "Sensitivity:".

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P2.Heading.autoforwarded

               If it is set to FALSE, it is simply mapped to the
               extended RFC 822 field "Autoforwarded:".  If this is set
               to TRUE, the P2.Body does not consist of a single
               P2.ForwardedIPMessage, then there is an X.400 error, and
               the message should be bounced.  Otherwise the following
               steps are taken.

                  1.  The mappings for all of the message, except the
                      body part are completed.

                  2.  Prepend each RFC 822 fieldname with the string
                      "Autoforwarded-". Mapped to the extended RFC 822
                      field "Autoforwarded:".

                  3.  Add the field "Autoforwarded:" with value TRUE.

                  4.  Convert the syntax of the P2.ForwardedIPMessage to
                      generate the remaining RFC 822 fields.

         The P2.Body is mapped into the RFC 822 message body.  Each
         P2.BodyPart is converted to ASCII.  If the P2.Body contains a
         P2.BodyPart not listed here, the entire message should be
         rejected.  If there are exactly two P2.IA5Text body parts, and
         the first line of the first is "RFC-822-Headers:", then the
         rest of this first body part should be treated as additional
         header information for the RFC 822 message.  If there is an
         "In-Reply-To:" field, this should be used to replace any
         generated In-Reply-To: field.

         In other cases of multiple P2.BodyPart, the mapping defined by
         Rose and Stefferud in [Rose85b], should be used to separate the
         P2.BodyParts in the single RFC 822 message body.

         Individual body parts are mapped as follows:

            P2.IA5Text

               The mapping is trivial.

            P2.TTX

               If any P1.Teletex.NonBasicParams are set, the message
               should be rejected.  Otherwise, it should be converted to
               ASCII according to chapter 3.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

            P2.SFD

               An SFD should be converted to ASCII as if it was being
               rendered on an 79 column ASCII only VDU.  It seems likely
               that many gateways will not support this conversion.  In
               these cases, the message should be rejected.

            P2.ForwardedIPMessage

               The P2.ForwardedIPMessage.delivery and
               P2.ForwardedIPMessage.DeliveryInformation are
               discarded <9>.  The IM-UAPDU should have its syntax
               mapped (recursively) according to this gatewaying
               specification.  Clearly, it makes no sense to apply any
               of the actions defined here.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix A -- Quoted String Encodings

   This Appendix describes a quoting mechanism which may be used to
   allow general interworking between RFC 822, and variants of RFC 822
   which do not support 822.quoted-string.  This is important, as the
   basic X.400 <-> RFC 822 mapping makes use of 822.quoted-string.

   1.  ASCII <-> 822.atom

      The following EBNF is specified.

         atom-encoded    = *( a-char / a-encoded-char )
         a-char          = <any CHAR except specials, SPACE,
                                 CTL, "_", and "#">
         a-encoded-char  = "_"                   ; (space)
                         / "#u#"                 ; (_)
                         / "#l#"                 ; <(>
                         / "#r#"                 ; <)>
                         / "#m#"                 ; (,)
                         / "#c#"                 ; (:)
                         / "#b#"                 ; (\)
                         / "#h#"                 ; (#)
                         / "#e#"                 ; ($=)
                         / "#s#"                 ; ($/)
                         / "#" 3DIGIT "#"

      NOTE: There are two encodings of double characters.  This is so
      that systems using this encoding, do not also need to know about
      the "$" quoting mechanism defined in chapter 4.

      The 822.3DIGIT in EBNF.a-encoded-char must have range 0-127
      (Decimal), and is interpreted in decimal as the corresponding
      ASCII character.  The choice of special abbreviations (as opposed
      to octal encoding) provided is based on the manner in which this
      mapping is most frequently used: encoding PrintableString
      components of O/R names as atom.  Therefore, there are special
      encodings for each of the PrintableString characters not in
      EBNF.a-char, except ".".  Space is given a single character
      encoding, due to its (expected) frequency of use, and backslash as
      the RFC 822 single quote character.

      To encode (ASCII -> atom): all EBNF.a-char are used directly and
      all other CHAR are encoded as EBNF.a-encoded-char.  To decode
      (822.atom -> ASCII): if 822.atom can be parsed as
      EBNF.encoded-atom reverse the previous mapping.  If it cannot be
      so parsed, map the characters directly.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   2.  822.local-part <-> ASCII

      A related transformation is for 822.local-part (or other element
      defined as '822.word ("." 822.word)') where not 822.quoted-text is
      used.  To encode (ASCII -> 822.local-part), all EBNF.a-char and
      "." are used directly and all other 822.CHAR are encoded as
      EBNF.a-encoded-char.  To decode (822.local-part -> ASCII), first
      attempt to parse 822.local-part as '822.atom *("." 822.atom)'.  If
      this fails, or if each 822.atom cannot be parsed as
      EBNF.atom-encoded then map each character directly.  Otherwise map
      each "." directly, and each atom as in the previous section.

      There are places where it is needed to convert between
      PrintableString or IA5Text (X.400), and 822.word (RFC 822).  word
      may be encoded as 822.atom (which has a restricted character set)
      or as 822.quoted-string, which can handle all ASCII characters.
      If 822.quoted-string is used, clearly the mappings for
      PrintableString defined in Chapter 3 provide a straightforward
      mapping.  However, some RFC 822 based networks cannot handle the
      822.quoted-string format in all cases.  This Appendix is for use
      in these cases.  The major requirement for this mapping is the
      UNIX world, but it may well be needed in other places.

      These mappings are somewhat artificial, and their usage is
      discouraged, except in cases where there is no alternative.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix B -- Mappings Specific to JNT Mail

   This Appendix is specific to the JNT Mail Protocol.  It describes
   specific changes in the context of this protocol.  Addressing is not
   discussed here, as it is covered in Appendix A.

   1.  Introduction

      There are four aspects of a gateway which are JNT Mail Specific,
      in addition to those relating to addressing.  These are each given
      a section of this appendix.

   2.  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.

      When going from JNT Mail to X.400, the User Report Request bits of
      each P1.RecipientInfo.perRecipientFlag should be set to confirmed.
      If there is more that one address in the Acknowledge-To: field, or
      if the one address is not equivalent to the 822-P1 return address,
      then:

         a.   Acknowledgement(s) should be generated by the gateway.
              The text of these acknowledgements should indicate that
              they are generated by the gateway.

         b.   The Acknowledge-To: field should also be passed in the
              first P2.BodyPart.

      When going from X.400 to JNT Mail, in cases where
      P1.RecipientInfo.perRecipientFlag has the user bits set to
      confirmed the copy of the message to that recipient should have an
      Acknowledge-To: field containing the P.UMPDUEnvelope.originator.
      No attempt should be made to map Receipt notification requests
      onto Acknowledge-To:.  This is because no association can be
      guaranteed between P2 and P1 level addressing information.

   3.  Trace

      JNT Mail trace uses the Via: syntax.  When going from JNT Mail to
      X.400, the following mapping onto P1.TraceInformation is used.

         P1.DomainSuppliedInfo.action is set to relayed.

         P1.DomainSuppliedInfo.arrival is set to the date-time component

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

         of the Via: field.  P1.DomainSuppliedInfo.previous has
         P1.CountryName as a null string, and
         P1.AdministrationDomainName as the domain specified in the Via:
         field.
         P1.TraceInformation.GlobalDomainIdentifier has P1.CountryName
         as a null string, and P1.AdministrationDomainName as any
         commented information in the Via: field.  For example:

            Via: UK.AC.Edinburgh ; 17 Jun 85 9:15:29 BST (EMAS V7)

            maps to -

            P1.GlobalDomainIdentifier
               CountryName                  = ""
               AdministrationDomainName     = "(EMAS V7)"
            P1.DomainSuppliedInfo
               arrival                      = 17 Jun 85 9:15:29 BST
               action                       = relayed
               previous
                  CountryName               = ""
                  AdministrationDomainName  = "UK.AC.Edinburgh"

   4.  Timezone specification

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

   5.  Lack of separate 822-P1 originator specification

      In JNT Mail the default mapping of the P1.MPDUEnvelope.originator
      is to the Sender: field.  This can cause a problem if the mapping
      of P2.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 P2.heading.authorisingUsers component and
      P2.Heading.originator.ORName is different from
      P1.UMPDUEnvelope.originator, map P1.MPDUEnvelope.originator onto
      the Sender: field.

      If an IPM has a P2.heading.authorisingUsers component, and
      P2.Heading.originator.ORName is different from
      P1.UMPDUEnvelope.originator, P1.MPDUEnvelpoe.originator should be

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

      mapped onto the Sender: field, and P2.Heading.originator mapped
      onto the Original-Sender: field.

      In other cases the P1.MPDUEnvelope.Originator is already correctly
      represented.

      Note that in some pathological cases, this mapping is
      asymmetrical.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix C -- Mappings Specific to Internet Mail

   The Simple Mail Transfer Protocol [Postel82a] is used in the
   ARPA-Internet, and in any network following the US DoD standards for
   internetwork protocols.  This appendix is specific to those hosts
   which use SMTP to exchange mail.

   1.   Mapping between O/R names and SMTP addresses

      The mappings of Chapter 4 are to be used.

   2.   Use of the ARPA Domain System

      Whenever possible, domain-qualified addresses should be be used to
      specify encoded O/R names.  These domain encodings naturally
      should be independent of any routing information.

   3.   Identification of gateways

      The ARPA-Internet Network Information Center (NIC) will maintain a
      list of registered X.400 gateways in the ARPA Internet.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix D -- Mappings Specific to Phonenet Mail

   There are currently no mappings specific to Phonenet Mail.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix E -- 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) [Horton86a] and then
   gatewaying the resulting RFC 822 address into X.400.  For example, an
   X.400 address

      Country         US
      Organization    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 thought a pair of
   gateways:

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

   or through a single X.400 to UUCP gateway:

      Country         US
      ADMD            ATT
      PRMD            UUCP
      Organization    GateOrg
      UUCP            inthop!dest!user

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Appendix F -- Format of Address Mapping Tables

   There is a need to specify the association between the domain and
   X.400 namespaces described in 4.2.1.  This is defined as a table
   syntax, but the syntax is defined in a manner which makes it suitable
   for use with domain nameservers (such as the DARPA Domain nameservers
   or the UK NRS).  The symmetry of the mapping is not clear, so a
   separate table is specified for each direction.  For domain -> X.400:

      domain-syntax "#" dmn-orname "#"

      For example:

      AC.UK#PRMD$DES.ADMD$BT.C$UK#
      XEROX.COM#O$Xerox.ADMD$ATT.C$US#

   For X.400 -> domain:

      dmn-orname "#" domain-syntax "#"

   EBNF.domain-syntax will be interpreted according to RFC 920.
   EBNF.dmn-orname will have components ordered as defined in section
   4.2.1, and with the most significant component on the RHS.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

References

   Bonacker85a.

      K.H. Bonacker, U. Pankoke-Babatz, and H. Santo, "EAN - Conformity
      to X.400 and DFN-Pflichtenheft," GMD (Gesellschaft fur Mathematik
      und Datenverarbeitung) report, June 1985.

   CCITT84a.

      CCITT SG 5/VII, "Recommendations X.400," Message Handling Systems:
      System Model - Service Elements, October 1984.

   CCITT84b.

      CCITT SG 5/VII, "Recommendations X.411," Message Handling Systems:
      Message Transfer Layer, October 1984.

   CCITT84c.

      CCITT SG 5/VII, "Recommendations X.420," Message Handling Systems:
      Interpersonal Messaging User Agent Layer, October 1984.

   CCITT84d.

      CCITT SG 5/VII, "Recommendations X.409," Message Handling Systems:
      Presentation Transfer Syntax and Notation, October 1984.

   CEN/CENELEC/85a.

      CEN/CENELEC/Information Technology/Working Group on Private
      Message Handling Systems, "FUNCTIONAL STANDARD A/3222,"
      CEN/CLC/IT/WG/PMHS N 17, October 1985.

   Crocker82a.

      D.H. Crocker, "Standard of the Format of ARPA Internet Text
      Messages," RFC 822, August 1982.

   Horton85a.

      M.R. Horton, "Draft Standard for ARPA/MHS Addressing Gateways,"
      AT&T Bell Laboratories, October 1985.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   Horton86a.

      M.R. Horton, "UUCP Mail Interchange Format Standard", RFC 976,
      February 1986.

   ICL84a.

      ICL, "Comparison of service elements of Grey Book Mail and X.400,"
      Mailgroup Note 18: Extract from unpublished report for ITSU
      (Information Technology Standards Unit), July 1984.

   Kille84a.

      S.E. Kille, (editor), JNT Mail Protocol (revision 1.0), Joint
      Network Team, Rutherford Appleton Laboratory, March 1984.

   Kille84b.

      S.E. Kille, "Gatewaying between RFC 822 and JNT Mail," JNT
      Mailgroup Note 15, May 1984.

   Kille86a.

      S.E. Kille, "O/R Names in the UK Academic Community," UK Working
      Document, March 1986.

   Larmouth83a.

      J. Larmouth, "JNT Name Registration Technical Guide," Salford
      University Computer Centre, April 1983.

   Neufeld85a.

      G. Neufeld, J. Demco, B. Hilpert, and R. Sample, "EAN: an X.400
      message system," in Second International Symposium on Computer
      Message Systems, Washington, pp. 1-13, North Holland,
      September 1985.

   Postel82a.

      J. Postel, "Simple Mail Transfer Protocol," RFC 821, August 1982.

   Postel84a.

      J. Postel and J. Reynolds, "Domain Requirements," RFC 920,
      October 1984.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

   Rose85a.

      M.T. Rose, "Mapping Service Elements between ARPA and MHS," Draft
      proposal, October 1985.

   Rose85b.

      M.T. Rose and E.A. Stefferud, "Proposed Standard for Message
      Encapsulation," RFC 934, January 1985.

RFC 987                                                        June 1986
Mapping between X.400 and RFC 822

Notes:

   <0>  UNIX is a trademark of Bell Laboratories.

   <1>  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.  (Sometime called
        a "mail relay".)

   <2>  If the remote protocol is JNT Mail, a notification may also be
        sent by the recipient UA.

   <3>  The asymmetry occurs where an ASCII string contains the sequence
        EBNF.ps-encoded-char.  This would be mapped directly to
        PrintableString, but the reverse mapping would be to the value
        implied by the sequence.

   <4>  It might be suggested that for reasons of elegance,
        EBNF.ps-delim (left parenthesis) is encoded as
        EBNF.ps-encoded-char. This is not done, as it it would never be
        possible to represent a PrintableString containing the character
        "(" in ASCII.  This is because an "(" in ASCII would be mapped
        to the encoding in PrintableString.

   <5>  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.

   <6>  P2.ORname is defined as P1.ORName.

   <7>  This recommendation may change in the light of CCITT or
        CEN/CENELEC guidelines on the use of initials.

   <8>  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.

   <9>  Although this violates chapter 1, part 4, principles 2 and 3, it
        is suggested that this is justified by principle 1.

 

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