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RFC 2298 - An Extensible Message Format for Message Disposition


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Network Working Group                                          R. Fajman
Request for Comments: 2298                 National Institutes of Health
Category: Standards Track                                     March 1998

                      An Extensible Message Format
                 for Message Disposition Notifications

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This memo defines a MIME content-type that may be used by a mail user
   agent (UA) or electronic mail gateway to report the disposition of a
   message after it has been sucessfully delivered to a recipient.  This
   content-type is intended to be machine-processable.  Additional
   message headers are also defined to permit Message Disposition
   Notifications (MDNs) to be requested by the sender of a message.  The
   purpose is to extend Internet Mail to support functionality often
   found in other messaging systems, such as X.400 and the proprietary
   "LAN-based" systems, and often referred to as "read receipts,"
   "acknowledgements," or "receipt notifications."  The intention is to
   do this while respecting the privacy concerns that have often been
   expressed when such functions have been discussed in the past.

   Because many messages are sent between the Internet and other
   messaging systems (such as X.400 or the proprietary "LAN-based"
   systems), the MDN protocol is designed to be useful in a multi-
   protocol messaging environment.  To this end, the protocol described
   in this memo provides for the carriage of "foreign" addresses, in
   addition to those normally used in Internet Mail.  Additional
   attributes may also be defined to support "tunneling" of foreign
   notifications through Internet Mail.

Table of Contents

   1.   Introduction ............................................  2
   2.   Requesting Message Disposition Notifications ............  3
   3.   Format of a Message Disposition Notification ............  7
   4.   Timeline of events ...................................... 17
   5.   Conformance and Usage Requirements ...................... 18
   6.   Security Considerations ................................. 19
   7.   Collected Grammar ....................................... 20
   8.   Guidelines for Gatewaying MDNs .......................... 22
   9.   Example ................................................. 24
   10.  IANA Registration Forms ................................. 25
   11.  Acknowledgments ......................................... 26
   12.  References .............................................. 26
   13.  Author's Address ........................................ 27
   14.  Copyright ............................................... 28

1.  Introduction

   This memo defines a MIME content-type [5] for message disposition
   notifications (MDNs).  An MDN can be used to notify the sender of a
   message of any of several conditions that may occur after successful
   delivery, such as display of the message contents, printing of the
   message, deletion (without display) of the message, or the
   recipient's refusal to provide MDNs.  The "message/disposition-
   notification" content-type defined herein is intended for use within
   the framework of the "multipart/report" content type defined in RFC
   1892 [7].

   This memo defines the format of the notifications and the RFC 822
   headers used to request them.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

1.1 Purposes

   The MDNs defined in this memo are expected to serve several purposes:

   (a)  Inform human beings of the disposition of messages after
        succcessful delivery, in a manner which is largely independent
        of human language;

   (b)  Allow mail user agents to keep track of the disposition of
        messages sent, by associating returned MDNs with earlier message
        transmissions;

   (c)  Convey disposition notification requests and disposition
        notifications between Internet Mail and "foreign" mail systems
        via a gateway;

   (d)  Allow "foreign" notifications to be tunneled through a MIME-
        capable message system and back into the original messaging
        system that issued the original notification, or even to a third
        messaging system;

   (e)  Allow language-independent, yet reasonably precise, indications
        of the disposition of a message to be delivered.

1.2 Requirements

   These purposes place the following constraints on the notification
   protocol:

   (a)  It must be readable by humans, as well as being machine-
        parsable.

   (b)  It must provide enough information to allow message senders (or
        their user agents) to unambiguously associate an MDN with the
        message that was sent and the original recipient address for
        which the MDN is issued (if such information is available), even
        if the message was forwarded to another recipient address.

   (c)  It must also be able to describe the disposition of a message
        independent of any particular human language or of the
        terminology of any particular mail system.

   (d)  The specification must be extensible in order to accomodate
        future requirements.

2.  Requesting Message Disposition Notifications

   Message disposition notifications are requested by including a
   Disposition-Notification-To header in the message.  Further
   information to be used by the recipient's UA in generating the MDN
   may be provided by including Original-Recipient and/or Disposition-
   Notification-Options headers in the message.

2.1 The Disposition-Notification-To Header

   A request that the receiving user agent issue message disposition
   notifications is made by placing a Disposition-Notification-To header
   into the message.  The syntax of the header, using the ABNF of RFC
   822 [2], is

     mdn-request-header = "Disposition-Notification-To" ":" 1#mailbox

   The mailbox token is as specified in RFC 822 [2].

   The presence of a Disposition-Notification-To header in a message is
   merely a request for an MDN.  The recipients' user agents are always
   free to silently ignore such a request.  Alternatively, an explicit
   denial of the request for information about the disposition of the
   message may be sent using the "denied" disposition in an MDN.

   An MDN MUST NOT itself have a Disposition-Notification-To header.
   An MDN MUST NOT be generated in response to an MDN.

   At most one MDN may be issued on behalf of each particular recipient
   by their user agent.  That is, once an MDN has been issued on behalf
   of a recipient, no further MDNs may be issued on behalf of that
   recipient, even if another disposition is performed on the message.
   However, if a message is forwarded, an MDN may been issued for the
   recipient doing the forwarding and the recipient of the forwarded
   message may also cause an MDN to be generated.

   While Internet standards normally do not specify the behavior of user
   interfaces, it is strongly recommended that the user agent obtain the
   user's consent before sending an MDN.  This consent could be obtained
   for each message through some sort of prompt or dialog box, or
   globally through the user's setting of a preference.  The user might
   also indicate globally that MDNs are never to be sent or that a
   "denied" MDN is always sent in response to a request for an MDN.

   MDNs SHOULD NOT be sent automatically if the address in the
   Disposition-Notification-To header differs from the address in the
   Return-Path header (see RFC 822 [2]).  In this case, confirmation
   from the user SHOULD be obtained, if possible.  If obtaining consent
   is not possible (e.g., because the user is not online at the time),
   then an MDN SHOULD NOT be sent.

   Confirmation from the user SHOULD be obtained (or no MDN sent) if
   there is no Return-Path header in the message, or if there is more
   than one distinct address in the Disposition-Notification-To header.

   The comparison of the addresses should be done using only the addr-
   spec (local-part "@" domain) portion, excluding any phrase and route.
   The comparison MUST be case-sensitive for the local-part and case-
   insensitive for the domain part.

   If the message contains more than one Return-Path header, the
   implementation may pick one to use for the comparison, or treat the
   situation as a failure of the comparison.

   The reason for not automatically sending an MDN if the comparison
   fails or more than one address is specified is to reduce the
   possibilities for mail loops and use of MDNs for mail bombing.

   A message that contains a Disposition-Notification-To header SHOULD
   also contain a Message-ID header as specified in RFC 822 [2].  This
   will permit automatic correlation of MDNs with original messages by
   user agents.

   If it is desired to request message disposition notifications for
   some recipients and not others, two copies of the message should be
   sent, one with an Disposition-Notification-To header and one without.
   Many of the other headers of the message (e.g., To, cc) will be the
   same in both copies.  The recipients in the respective message
   envelopes determine for whom message disposition notifications are
   requested and for whom they are not.  If desired, the Message-ID
   header may be the same in both copies of the message.  Note that
   there are other situations (e.g., bcc) in which it is necessary to
   send multiple copies of a message with slightly different headers.
   The combination of such situations and the need to request MDNs for a
   subset of all recipients may result in more than two copies of a
   message being sent, some with a Disposition- Notification-To header
   and some without.

   Messages posted to newsgroups SHOULD NOT have a Disposition-
   Notification-To header.

2.2 The Disposition-Notification-Options Header

   Future extensions to this specification may require that information
   be supplied to the recipient's UA for additional control over how and
   what MDNs are generated.  The Disposition-Notification-Options header
   provides an extensible mechanism for such information.  The syntax of
   this header, using the ABNF of RFC 822 [2], is

     Disposition-Notification-Options =
          "Disposition-Notification-Options" ":"
          disposition-notification-parameters

     disposition-notification-parameters = parameter *(";" parameter)

     parameter = attribute "=" importance "," 1#value

     importance = "required" / "optional"

   The definitions of attribute and value are as in the definition of
   the Content-Type header in RFC 2045 [4].

   An importance of "required" indicates that interpretation of the
   parameter is necessary for proper generation of an MDN in response to
   this request.  If a UA does not understand the meaning of the
   parameter, it MUST NOT generate an MDN with any disposition type
   other than "failed" in response to the request.  An importance of
   "optional" indicates that a UA that does not understand the meaning
   of this parameter MAY generate an MDN in response anyway, ignoring
   the value of the parameter.

   No parameters are defined in this specification.  Parameters may be
   defined in the future by later revisions or extensions to this
   specification.  Parameter attribute names beginning with "X-" will
   never be defined as standard names; such names are reserved for
   experimental use.  MDN parameter names not beginning with "X-" MUST
   be registered with the Internet Assigned Numbers Authority (IANA) and
   described in a standards-track RFC or an experimental RFC approved by
   the IESG.  See Section 10 for a registration form.

   If a required parameter is not understood or contains some sort of
   error, the receiving UA SHOULD issue an MDN with a disposition type
   of "failed" (see Section 3.2.6) and include a Failure field (see
   Section 3.2.7) that further describes the problem.  MDNs with the a
   disposition type of "failed" and a "Failure" field MAY also be
   generated when other types of errors are detected in the parameters
   of the Disposition-Notification-Options header.

   However, an MDN with a disposition type of "failed" MUST NOT be
   generated if the user has indicated a preferance that MDNs are not to
   be sent.  If user consent would be required for an MDN of some other
   disposition type to be sent, user consent SHOULD also be obtained
   before sending an MDN with a disposition type of "failed".

2.3 The Original-Recipient Header

   Since electronic mail addresses may be rewritten while the message is
   in transit, it is useful for the original recipient address to be
   made available by the delivering MTA.  The delivering MTA may be able
   to obtain this information from the ORCPT parameter of the SMTP RCPT
   TO command, as defined in RFC 1891 [8].  If this information is
   available, the delivering MTA SHOULD insert an Original-Recipient
   header at the beginning of the message (along with the Return-Path
   header).  The delivering MTA MAY delete any other Original-Recipient
   headers that occur in the message.  The syntax of this header, using
   the ABNF of RFC 822 [2], is as follows

     original-recipient-header =
          "Original-Recipient" ":" address-type ";" generic-address

   The address-type and generic-address token are as as specified in the
   description of the Original-Recipient field in section 3.2.3.

   The purpose of carrying the original recipient information and
   returning it in the MDN is to permit automatic correlation of MDNs
   with the original message on a per-recipient basis.

2.4 Use with the Message/Partial Content Type

   The use of the headers Disposition-Notification-To, Disposition-
   Notification-Options, and Original-Recipient with the MIME
   Message/partial content type (RFC 2046 [5]) requires further
   definition.

   When a message is segmented into two or more message/partial
   fragments, the three headers mentioned in the above paragraph SHOULD
   be placed in the "inner" or "enclosed" message (using the terms of
   RFC 2046 [5]).  These headers SHOULD NOT be used in the headers of
   any of the fragments themselves.

   When the multiple message/partial fragments are reassembled, the
   following applies.  If these headers occur along with the other
   headers of a message/partial fragment message, they pertain to an MDN
   to be generated for the fragment.  If these headers occur in the
   headers of the "inner" or "enclosed" message (using the terms of RFC
   2046 [5]), they pertain to an MDN to be generated for the reassembled
   message.  Section 5.2.2.1 of RFC 2046 [5]) is amended to specify
   that, in addition to the headers specified there, the three headers
   described in this specification are to be appended, in order, to the
   headers of the reassembled message.  Any occurances of the three
   headers defined here in the headers of the initial enclosing message
   must not be copied to the reassembled message.

3.  Format of a Message Disposition Notification

   A message disposition notification is a MIME message with a top-
   level content-type of multipart/report (defined in RFC 1892 [7]).
   When a multipart/report content is used to transmit an MDN:

   (a)  The report-type parameter of the multipart/report content is
        "disposition-notification".

   (b)  The first component of the multipart/report contains a human-
        readable explanation of the MDN, as described in RFC 1892 [7].

   (c)  The second component of the multipart/report is of content-type
        message/disposition-notification, described in section 3.1 of
        this document.

   (d)  If the original message or a portion of the message is to be
        returned to the sender, it appears as the third component of the
        multipart/report.  The decision of whether or not to return the
        message or part of the message is up to the UA generating the
        MDN.  However, in the case of encrypted messages requesting
        MDNs, encrypted message text MUST be returned, if it is returned
        at all, only in its original encrypted form.

        NOTE:  For message dispostion notifications gatewayed from
        foreign systems, the headers of the original message may not be
        available.  In this case the third component of the MDN may be
        omitted, or it may contain "simulated" RFC 822 headers which
        contain equivalent information.  In particular, it is very
        desirable to preserve the subject and date fields from the
        original message.

   The MDN MUST be addressed (in both the message header and the
   transport envelope) to the address(es) from the Disposition-
   Notification-To header from the original message for which the MDN is
   being generated.

   The From field of the message header of the MDN MUST contain the
   address of the person for whom the message disposition notification
   is being issued.

   The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
   null (<>), specifying that no Delivery Status Notification messages
   or other messages indicating successful or unsuccessful delivery are
   to be sent in response to an MDN.

   A message disposition notification MUST NOT itself request an MDN.
   That is, it MUST NOT contain a Disposition-Notification-To header.

   The Message-ID header (if present) for an MDN MUST be different from
   the Message-ID of the message for which the MDN is being issued.

   A particular MDN describes the disposition of exactly one message for
   exactly one recipient.  Multiple MDNs may be generated as a result of
   one message submission, one per recipient.  However, due to the
   circumstances described in Section 2.1, MDNs may not be generated for
   some recipients for which MDNs were requested.

3.1 The message/disposition-notification content-type

   The message/disposition-notification content-type is defined as
   follows:

     MIME type name:                message

     MIME subtype name:             disposition-notification
     Optional parameters:           none
     Encoding considerations:       "7bit" encoding is sufficient and
                                    MUST be used to maintain readability
                                    when viewed by non-MIME mail
                                    readers.
     Security considerations:       discussed in section 6 of this memo.

   The message/disposition-notification report type for use in the
   multipart/report is "disposition-notification".

   The body of a message/disposition-notification consists of one or
   more "fields" formatted according to the ABNF of RFC 822 header
   "fields" (see [2]).  Using the ABNF of RFC 822, the syntax of the
   message/disposition-notification content is as follows:

     disposition-notification-content = [ reporting-ua-field CRLF ]
          [ mdn-gateway-field CRLF ]
          [ original-recipient-field CRLF ]
          final-recipient-field CRLF
          [ original-message-id-field CRLF ]
          disposition-field CRLF
          *( failure-field CRLF )
          *( error-field CRLF )
          *( warning-field CRLF )
          *( extension-field CRLF )

3.1.1 General conventions for fields

   Since these fields are defined according to the rules of RFC 822 [2],
   the same conventions for continuation lines and comments apply.
   Notification fields may be continued onto multiple lines by beginning
   each additional line with a SPACE or HTAB.  Text which appears in
   parentheses is considered a comment and not part of the contents of
   that notification field.  Field names are case-insensitive, so the
   names of notification fields may be spelled in any combination of
   upper and lower case letters.  Comments in notification fields may
   use the "encoded-word" construct defined in RFC 2047 [6].

3.1.2 "*-type" subfields

   Several fields consist of a "-type" subfield, followed by a semi-
   colon, followed by "*text".  For these fields, the keyword used in
   the address-type or MTA-type subfield indicates the expected format
   of the address or MTA-name that follows.

   The "-type" subfields are defined as follows:

   (a)  An "address-type" specifies the format of a mailbox address.
        For example, Internet Mail addresses use the "rfc822" address-
        type.

         address-type = atom

   (b)  An "MTA-name-type" specifies the format of a mail transfer
        agent name.  For example, for an SMTP server on an Internet
        host, the MTA name is the domain name of that host, and the
        "dns" MTA-name-type is used.

         mta-name-type = atom

   Values for address-type and mta-name-type are case-insensitive.  Thus
   address-type values of "RFC822" and "rfc822" are equivalent.

   The Internet Assigned Numbers Authority (IANA) will maintain a
   registry of address-type and mta-name-type values, along with
   descriptions of the meanings of each, or a reference to a one or more
   specifications that provide such descriptions.  (The "rfc822"
   address-type is defined in RFC 1891 [8].) Registration forms for
   address-type and mta-name-type appear in RFC 1894 [9].

   IANA will not accept registrations for any address-type name that
   begins with "X-".  These type names are reserved for experimental
   use.

3.1.3 Lexical tokens imported from RFC 822

   The following lexical tokens, defined in RFC 822 [2], are used in the
   ABNF grammar for MDNs:  atom, CRLF, mailbox, msg-id, text.

3.2 Message/disposition-notification Fields

3.2.1 The Reporting-UA field

     reporting-ua-field = "Reporting-UA" ":" ua-name
                          [ ";" ua-product ]

     ua-name = *text

     ua-product = *text

   The Reporting-UA field is defined as follows:

   A MDN describes the disposition of a message after it has been
   delivered to a recipient.  In all cases, the Reporting-UA is the UA
   that performed the disposition described in the MDN.  This field is

   optional, but recommended.  For Internet Mail user agents, it is
   recommended that this field contain both the DNS name of the
   particular instance of the UA that generated the MDN and the name of
   the product.  For example,

     Reporting-UA:  rogers-mac.dcrt.nih.gov; Foomail 97.1

   If the reporting UA consists of more than one component (e.g., a base
   program and plug-ins), this may be indicated by including a list of
   product names.

3.2.2 The MDN-Gateway field

   The MDN-Gateway field indicates the name of the gateway or MTA that
   translated a foreign (non-Internet) message disposition notification
   into this MDN.  This field MUST appear in any MDN which was
   translated by a gateway from a foreign system into MDN format, and
   MUST NOT appear otherwise.

        mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name

        mta-name = *text

   For gateways into Internet Mail, the MTA-name-type will normally be
   "smtp", and the mta-name will be the Internet domain name of the
   gateway.

3.2.3 Original-Recipient field

   The Original-Recipient field indicates the original recipient address
   as specified by the sender of the message for which the MDN is being
   issued.  For Internet Mail messages the value of the

   Original-Recipient field is obtained from the Original-Recipient
   header from the message for which the MDN is being generated.  If
   there is no Original-Recipient header in the message, then the
   Original-Recipient field MUST be omitted, unless the same information
   is reliably available some other way.  If there is an Original-
   Recipient header in the original message (or original recipient
   information is reliably available some other way), then the
   Original-Recipient field must be supplied.  If there is more than one
   Original-Recipient header in the message, the UA may choose the one
   to use or act as if no Original-Recipient header is present.

     original-recipient-field =
          "Original-Recipient" ":" address-type ";" generic-address

     generic-address = *text

   The address-type field indicates the type of the original recipient
   address.  If the message originated within the Internet, the
   address-type field field will normally be "rfc822", and the address
   will be according to the syntax specified in RFC 822 [2].  The value
   "unknown" should be used if the Reporting UA cannot determine the
   type of the original recipient address from the message envelope.
   This address is the same as that provided by the sender and can be
   used to automatically correlate MDN reports with original messages on
   a per recipient basis.

3.2.4 Final-Recipient field

   The Final-Recipient field indicates the recipient for which the MDN
   is being issued.  This field MUST be present.

   The syntax of the field is as follows:

     final-recipient-field =
          "Final-Recipient" ":" address-type ";" generic-address

   The generic-address subfield of the Final-Recipient field MUST
   contain the mailbox address of the recipient (from the From header of
   the MDN) as it was when the MDN was generated by the UA.

   The Final-Recipient address may differ from the address originally
   provided by the sender, because it may have been transformed during
   forwarding and gatewaying into an totally unrecognizable mess.
   However, in the absence of the optional Original-Recipient field, the
   Final-Recipient field and any returned content may be the only
   information available with which to correlate the MDN with a
   particular message recipient.

   The address-type subfield indicates the type of address expected by
   the reporting MTA in that context.  Recipient addresses obtained via
   SMTP will normally be of address-type "rfc822".

   Since mailbox addresses (including those used in the Internet) may be
   case sensitive, the case of alphabetic characters in the address MUST
   be preserved.

3.2.5 Original-Message-ID field

   The Original-Message-ID field indicates the message-ID of the message
   for which the MDN is being issued.  It is obtained from the Message-
   ID header of the message for which the MDN is issued.  This field
   MUST be present if the original message contained a Message-ID
   header.  The syntax of the field is

        original-message-id-field = "Original-Message-ID" ":" msg-id

   The msg-id token is as specified in RFC 822 [2].

3.2.6 Disposition field

   The Disposition field indicates the action performed by the
   Reporting-UA on behalf of the user.  This field MUST be present.

   The syntax for the Disposition field is:

     disposition-field = "Disposition" ":" disposition-mode ";"
                         disposition-type
                         [ '/' disposition-modifier
                           *( "," dispostion-modifier ) ]

     disposition-mode = action-mode "/" sending-mode

     action-mode = "manual-action" / "automatic-action"

     sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"

     disposition-type = "displayed"
                      / "dispatched"
                      / "processed"
                      / "deleted"
                      / "denied"
                      / "failed"

     disposition-modifier = ( "error" / "warning" )
                          / ( "superseded" / "expired" /
                              "mailbox-terminated" )
                          / disposition-modifier-extension

     disposition-modifier-extension = atom

   The disposition-mode, disposition-type and disposition-modifier may
   be spelled in any combination of upper and lower case characters.

3.2.6.1 Disposition modes

   The following disposition modes are defined:

   "manual-action"            The disposition described by the
                              disposition type was a result of an
                              explicit instruction by the user rather
                              than some sort of automatically performed
                              action.

   "automatic-action"         The disposition described by the
                              disposition type was a result of an
                              automatic action, rather than an explicit
                              instruction by the user for this message.

                              "Manual-action" and "automatic-action" are
                              mutually exclusive.  One or the other must
                              be specified.

   "MDN-sent-manually"        The user explicity gave permission for
                              this particular MDN to be sent.

   "MDN-sent-automatically"   The MDN was sent because the UA had
                              previously been configured to do so
                              automatically.

                              "MDN-sent-manually" and "MDN-sent-
                              automatically" are mutually exclusive.
                              One or the other must be specified.

3.2.6.2 Disposition types

   The following disposition-types are defined:

   "displayed"    The message has been displayed by the UA to someone
                              reading the recipient's mailbox.  There is
                              no guarantee that the content has been
                              read or understood.

   "dispatched"   The message has been sent somewhere in some manner
                              (e.g., printed, faxed, forwarded) without
                              necessarily having been previously
                              displayed to the user.  The user may or
                              may not see the message later.

   "processed"    The message has been processed in some manner (i.e.,
                              by some sort of rules or server) without
                              being displayed to the user.  The user may
                              or may not see the message later, or there
                              may not even be a human user associated
                              with the mailbox.

   "deleted"      The message has been deleted.  The recipient may or
                              may not have seen the message.  The
                              recipient might "undelete" the message at
                              a later time and read the message.

   "denied"       The recipient does not wish the sender to be informed
                              of the message's disposition.  A UA may
                              also siliently ignore message disposition
                              requests in this situation.

   "failed"       A failure occurred that prevented the proper
                              generation of an MDN.  More information
                              about the cause of the failure may be
                              contained in a Failure field.  The
                              "failed" disposition type is not to be
                              used for the situation in which there is
                              is some problem in processing the message
                              other than interpreting the request for an
                              MDN.  The "processed" or other disposition
                              type with appropriate disposition
                              modifiers is to be used in such
                              situations.

3.2.6.3 Disposition modifiers

   The following disposition modifiers are defined:

   "error"                            An error of some sort occurred
                                      that prevented successful
                                      processing of the message.
                                      Further information is contained
                                      in an Error field.

   "warning"                          The message was successfully
                                      processed but some sort of
                                      exceptional condition occurred.
                                      Further information is contained
                                      in a Warning field.

   "superseded"                       The message has been
                                      automatically rendered obsolete by
                                      another message received.  The
                                      recipient may still access and
                                      read the message later.

   "expired"                          The message has reached its
                                      expiration date and has been
                                      automatically removed from the
                                      recipient's mailbox.

   "mailbox-terminated"               The recipient's mailbox has been
                                      terminated and all message in it
                                      automatically removed.

                                      "Obsoleted", "expired", and
                                      "terminated" are to be used with
                                      the "deleted" disposition type and
                                      the "autoaction" and "autosent"
                                      disposition modifiers.

   disposition-modifier-extension     Additional disposition modifiers
                                      may be defined in the future by
                                      later revisions or extensions to
                                      this specification.  Disposition
                                      value names beginning with "X-"
                                      will never be defined as standard
                                      values; such names are reserved
                                      for experimental use.  MDN
                                      disposition value names NOT
                                      beginning with "X-" MUST be
                                      registered with the Internet
                                      Assigned Numbers Authority (IANA)
                                      and described in a standards-
                                      track RFC or an experimental RFC
                                      approved by the IESG.  See Section
                                      10 for a registration form.  MDNs
                                      with disposition modifier names
                                      not understood by the receiving UA
                                      MAY be silently ignored or placed
                                      in the user's mailbox without
                                      special inter- pretation.  They
                                      MUST not cause any error message
                                      to be sent to the sender of the
                                      MDN.

                                      If an UA developer does not wish
                                      to register the meanings of such
                                      disposition modifier extensions,
                                      "X-" modifiers may be used for
                                      this purpose.  To avoid name
                                      collisions, the name of the UA
                                      implementation should follow the
                                      "X-", (e.g. "X-Foomail-fratzed").

   It is not required that a UA be able to generate all of the possible
   values of the Disposition field.

   One and only one MDN may be issued on behalf of each particular
   recipient by their user agent.  That is, once an MDN has been issued
   on behalf of a recipient, no further MDNs may be issued on behalf of
   that recipient, even if another disposition is performed on the
   message.  However, if a message is forwarded, a "dispatched" MDN may

   been issued for the recipient doing the forwarding and the recipient
   of the forwarded message may also cause an MDN to be generated.

3.2.7 Failure, Error and Warning fields

   The Failure, Error and Warning fields are used to supply additional
   information in the form of text messages when the "failure"
   disposition type, "error" disposition modifier, and/or the "warning"
   disposition modifer appear.  The syntax is

     failure-field = "Failure" ":" *text

     error-field = "Error" ":" *text

     warning-field = "Warning" ":" *text

3.3 Extension fields

   Additional MDN fields may be defined in the future by later revisions
   or extensions to this specification.  Extension-field names beginning
   with "X-" will never be defined as standard fields; such names are
   reserved for experimental use.  MDN field names NOT beginning with
   "X-" MUST be registered with the Internet Assigned Numbers Authority
   (IANA) and described in a standards-track RFC or an experimental RFC
   approved by the IESG.  See Section 10 for a registration form.

   Extension MDN fields may be defined for the following reasons:

   (a)  To allow additional information from foreign disposition
        reports to be tunneled through Internet MDNs.  The names of such
        MDN fields should begin with an indication of the foreign
        environment name (e.g. X400-Physical-Forwarding-Address).

   (b)  To allow transmission of diagnostic information which is
        specific to a particular user agent (UA).  The names of such MDN
        fields should begin with an indication of the UA implementation
        which produced the MDN.  (e.g. Foomail-information).

   If an application developer does not wish to register the meanings of
   such extension fields, "X-" fields may be used for this purpose.  To
   avoid name collisions, the name of the application implementation
   should follow the "X-", (e.g. "X-Foomail-Log-ID" or "X-EDI-info").

4.  Timeline of events

   The following timeline shows when various events in the processing of
   a message and generation of MDNs take place:

   -- User composes message

   -- User tells UA to send message

   -- UA passes message to MTA (original recipient information
      passed along)

   -- MTA sends message to next MTA

   -- Final MTA receives message

   -- Final MTA delivers message to UA (possibily generating DSN)

   -- UA performs automatic processing and generates corresponding
      MDNs ("dispatched", "processed", "deleted", "denied" or "failed"
      disposition type with "automatic-action" and "MDN-sent-
      automatically" disposition modes)

   -- UA displays list of messages to user

   -- User selects a message and requests that some action be
      performed on it.

   -- UA performs requested action and, with user's permission,
      sends appropriate MDN ("displayed", "dispatched", "processed",
      "deleted", "denied" or "failed" disposition type with "manual-
      action" and "MDN-sent-manually" or "MDN-sent-automatically"
      disposition mode).

   -- User possibly performs other actions on message, but no
      further MDNs are generated.

5.  Conformance and Usage Requirements

   A UA or gateway conforms to this specification if it generates MDNs
   according to the protocol defined in this memo.  It is not necessary
   to be able to generate all of the possible values of the Disposition
   field.

   UAs and gateways MUST NOT generate the Original-Recipient field of an
   MDN unless the mail protocols provide the address originally
   specified by the sender at the time of submission.  Ordinary SMTP
   does not make that guarantee, but the SMTP extension defined in RFC
   1891 [8] permits such information to be carried in the envelope if it
   is available.  The Original-Recipient header defined in this document
   provides a way for the MTA to pass the original recipient address to
   the UA.

   Each sender-specified recipient address may result in more than one
   MDN.  If an MDN is requested for a recipient that is forwarded to
   multiple recipients of an "alias" (as defined in RFC 1891 [8],
   section 6.2.7.3), each of the recipients may issue an MDN.

   Successful distribution of a message to a mailing list exploder
   SHOULD be considered final disposition of the message.  A mailing
   list exploder may issue an MDN with a disposition type of "processed"
   and disposition modes of "automatic-action" and "MDN- sent-
   automatically" indicating that the message has been forwarded to the
   list.  In this case, the request for MDNs is not propogated to the
   members of the list.

   Alternaively, the mailing list exploder may issue no MDN and
   propogate the request for MDNs to all members of the list.  The
   latter behavior is not recommended for any but small, closely knit
   lists, as it might cause large numbers of MDNs to be generated and
   may cause confidential subscribers to the list to be revealed.  It is
   also permissible for the mailing list exploder to direct MDNs to
   itself, correlate them, and produce a report to the original sender
   of the message.

   This specification places no restrictions on the processing of MDNs
   received by user agents or mailing lists.

6.  Security Considerations

   The following security considerations apply when using MDNs:

6.1 Forgery

   MDNs may be forged as easily as ordinary Internet electronic mail.
   User agents and automatic mail handling facilities (such as mail
   distribution list exploders) that wish to make automatic use of MDNs
   should take appropriate precautions to minimize the potential damage
   from denial-of-service attacks.

   Security threats related to forged MDNs include the sending of:

   (a)  A falsified disposition notification when the indicated
        disposition of the message has not actually ocurred,

   (b)  Unsolicited MDNs

6.2 Confidentiality

   Another dimension of security is confidentiality.  There may be cases
   in which a message recipient does not wish the disposition of

   messages addressed to him to be known or is concerned that the
   sending of MDNs may reveal other confidential information (e.g., when
   the message was read).  In this situation, it is acceptable for the
   UA to issue "denied" MDNs or to silently ignore requests for MDNs.

   If the Disposition-Notification-To header is passed on unmodified
   when a message is distributed to the subscribers of a mailing list,
   the subscribers to the list may be revealed to the sender of the
   original message by the generation of MDNs.

   Headers of the original message returned in part 3 of the
   multipart/report could reveal confidential information about host
   names and/or network topology inside a firewall.

   An unencrypted MDN could reveal confidential information about an
   encrypted message, especially if all or part of the original message
   is returned in part 3 of the multipart/report.  Encrypted MDNs are
   not defined in this specification.

   In general, any optional MDN field may be omitted if the Reporting UA
   site or user determines that inclusion of the field would impose too
   great a compromise of site confidentiality.  The need for such
   confidentiality must be balanced against the utility of the omitted
   information in MDNs.

6.3 Non-Repudiation

   Within the framework of today's Internet Mail, the MDNs defined in
   this document provide valuable information to the mail user; however,
   MDNs can not be relied upon as a guarantee that a message was or was
   not not seen by the recipient.  Even if MDNs are not actively forged,
   they may be lost in transit.  The MDN issuing mechanism may be
   bypassed in some manner by the recipient.

7.  Collected Grammar

   NOTE:  The following lexical tokens are defined in RFC 822:  atom,
   CRLF, mailbox, msg-id, text.  The definitions of attribute and value
   are as in the definition of the Content-Type header in RFC 2045 [4].

   Message headers:

   mdn-request-header = "Disposition-Notification-To" ":" 1#mailbox

   Disposition-Notification-Options =
        "Disposition-Notification-Options" ":"
        disposition-notification-parameters

   disposition-notification-parameters = parameter *(";" parameter)

   parameter = attribute "=" importance "," 1#value

   importance = "required" / "optional"

   original-recipient-header =
        "Original-Recipient" ":" address-type ";" generic-address

   Report content:

   disposition-notification-content = [ reporting-ua-field CRLF ]
        [ mdn-gateway-field CRLF ]
        [ original-recipient-field CRLF ]
        final-recipient-field CRLF
        [ original-message-id-field CRLF ]
        disposition-field CRLF
        *( failure-field CRLF )
        *( error-field CRLF )
        *( warning-field CRLF )
        *( extension-field CRLF )

   address-type = atom

   mta-name-type = atom

   reporting-ua-field = "Reporting-UA" ":" ua-name
                        [ ";" ua-product ]

   ua-name = *text

   ua-product = *text

   mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name

   mta-name = *text

   original-recipient-field =
        "Original-Recipient" ":" address-type ";" generic-address

   generic-address = *text

   final-recipient-field =
        "Final-Recipient" ":" address-type ";" generic-address

   disposition-field = "Disposition" ":" disposition-mode ";"
                       disposition-type

                       [ '/' disposition-modifier
                         *( "," dispostion-modifier ) ]

   disposition-mode = action-mode "/" sending-mode

   action-mode = "manual-action" / "automatic-action"

   sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"

   disposition-type = "displayed"
                    / "dispatched"
                    / "processed"
                    / "deleted"
                    / "denied"
                    / "failed"

   disposition-modifier = ( "error" / "warning" )
                        / ( "superseded" / "expired" /
                            "mailbox-terminated" )
                        / disposition-modifier-extension

   disposition-modifier-extension = atom

   original-message-id-field = "Original-Message-ID" ":" msg-id

   failure-field = "Failure" ":" *text

   error-field = "Error" ":" *text

   warning-field = "Warning" ":" *text

   extension-field = extension-field-name ":" *text

   extension-field-name = atom

8.  Guidelines for Gatewaying MDNs

   NOTE:  This section provides non-binding recommendations for the
   construction of mail gateways that wish to provide semi-transparent
   disposition notifications between the Internet and another electronic
   mail system.  Specific MDN gateway requirements for a particular pair
   of mail systems may be defined by other documents.

8.1 Gatewaying from other mail systems to MDNs

   A mail gateway may issue an MDN to convey the contents of a "foreign"
   disposition notification over Internet Mail.  When there are
   appropriate mappings from the foreign notification elements to MDN

   fields, the information may be transmitted in those MDN fields.
   Additional information (such as might be needed to tunnel the foreign
   notification through the Internet) may be defined in extension MDN
   fields.  (Such fields should be given names that identify the foreign
   mail protocol, e.g. X400-* for X.400 protocol elements)

   The gateway must attempt to supply reasonable values for the
   Reporting-UA, Final-Recipient, and Disposition fields.  These will
   normally be obtained by translating the values from the foreign
   notification into their Internet-style equivalents.  However, some
   loss of information is to be expected.

   The sender-specified recipient address, and the original message-id,
   if present in the foreign notification, should be preserved in the
   Original-Recipient and Original-Message-ID fields.

   The gateway should also attempt to preserve the "final" recipient
   address from the foreign system.  Whenever possible, foreign protocol
   elements should be encoded as meaningful printable ASCII strings.

   For MDNs produced from foreign disposition notifications, the name of
   the gateway MUST appear in the MDN-Gateway field of the MDN.

8.2 Gatewaying from MDNs to other mail systems

   It may be possible to gateway MDNs from the Internet into a foreign
   mail system.  The primary purpose of such gatewaying is to convey
   disposition information in a form that is usable by the destination
   system.  A secondary purpose is to allow "tunneling" of MDNs through
   foreign mail systems, in case the MDN may be gatewayed back into the
   Internet.

   In general, the recipient of the MDN (i.e., the sender of the
   original message) will want to know, for each recipient:  the closest
   available approximation to the original recipient address, and the
   disposition (displayed, printed, etc.).

   If possible, the gateway should attempt to preserve the Original-
   Recipient address and Original-Message-ID (if present), in the
   resulting foreign disposition report.

   If it is possible to tunnel an MDN through the destination
   environment, the gateway specification may define a means of
   preserving the MDN information in the disposition reports used by
   that environment.

9.  Example

   NOTE:  This example is provided as illustration only, and is not
   considered part of the MDN protocol specification.  If the example
   conflicts with the protocol definition above, the example is wrong.

   Likewise, the use of *-type subfield names or extension fields in
   this example is not to be construed as a definition for those type
   names or extension fields.

9.1 This is an MDN issued after a message has been displayed to the user
   of an Internet Mail user agent.

   Date: Wed, 20 Sep 1995 00:19:00 (EDT) -0400
   From: Joe Recipient <Joe_Recipient@mega.edu>
   Message-Id: <199509200019.12345@mega.edu>
   Subject: Disposition notification
   To: Jane Sender <Jane_Sender@huge.com>
   MIME-Version: 1.0
   Content-Type: multipart/report; report-type=disposition-notification;
         boundary="RAA14128.773615765/mega.edu"

   --RAA14128.773615765/mega.edu

   The message sent on 1995 Sep 19 at 13:30:00 (EDT) -0400 to Joe
   Recipient <Joe_Recipient@mega.edu> with subject "First draft of
   report" has been displayed.  This is no guarantee that the message
   has been read or understood.

   --RAA14128.773615765/mega.edu
   content-type: message/disposition-notification

   Reporting-UA: joes-pc.cs.mega.edu; Foomail 97.1
   Original-Recipient: rfc822;Joe_Recipient@mega.edu
   Final-Recipient: rfc822;Joe_Recipient@mega.edu
   Original-Message-ID: <199509192301.23456@huge.com>
   Disposition: manual-action/MDN-sent-manually; displayed

   --RAA14128.773615765/mega.edu
   content-type: message/rfc822

   [original message goes here]

   --RAA14128.773615765/mega.edu--

10.  IANA Registration Forms

   The forms below are for use when registering a new parameter name for
   the Disposition-Notification-Options header, a new disposition
   modifier name, or a new MDN extension field.  Each piece of
   information required by a registration form may be satisfied either
   by providing the information on the form itself, or by including a
   reference to a published, publicly available specification that
   includes the necessary information.  IANA MAY reject registrations
   because of incomplete registration forms, imprecise specifications,
   or inappropriate names.

   To register, complete the applicable form below and send it via
   electronic mail to <IANA@IANA.ORG>.

10.1 IANA registration form for Disposition-Notification-Options header
   parameter names

   A registration for a Disposition-Notification-Options header
   parameter name MUST include the following information:

   (a) The proposed parameter name.

   (b) The syntax for parameter values, specified using BNF, ABNF,
   regular expressions, or other non-ambiguous language.

   (c) If parameter values are not composed entirely of graphic
   characters from the US-ASCII repertoire, a specification for how they
   are to be encoded as graphic US-ASCII characters in a Disposition-
   Notification-Options header.

   (d) A reference to a standards track RFC or experimental RFC approved
   by the IESG that describes the semantics of the parameter values.

10.2 IANA registration form for disposition modifer names

   A registration for a disposition-modifier name MUST include the
   following information:

   (a) The proposed disposition-modifier name.

   (b) A reference to a standards track RFC or experimental RFC approved
   by the IESG that describes the semantics of the disposition modifier.

10.3 IANA registration form for MDN extension field names

   A registration for an MDN extension field name MUST include the
   following information:

   (a) The proposed extension field name.

   (b) The syntax for extension values, specified using BNF, ABNF,
   regular expressions, or other non-ambiguous language.

   (c) If extension field values are not composed entirely of graphic
   characters from the US-ASCII repertoire, a specification for how they
   are to be encoded as graphic US-ASCII characters in a Disposition-
   Notification-Options header.

   (d) A reference to a standards track RFC or experimental RFC approved
   by the IESG that describes the semantics of the extension field.

11.  Acknowledgments

   This document is based on the Delivery Status Notifications document,
   RFC 1894 [9], by Keith Moore and Greg Vaudreuil.  Contributions were
   made by members of the IETF Receipt Working Group, including Harald
   Alverstrand, Ian Bell, Urs Eppenberger, Claus Andri Faerber, Ned
   Freed, Jim Galvin, Carl Hage, Mike Lake, Keith Moore, Paul Overell,
   Pete Resnick, Chuck Shih.

12.  References

   [1]   Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
         August 1982.

   [2]   Crocker, D., "Standard for the Format of ARPA Internet Text
         Messages", STD 11, RFC 822, August 1982.

   [3]   Braden, R. (ed.), "Requirements for Internet Hosts -
         Application and Support", STD 3, RFC 1123, October 1989.

   [4]   Freed, N., and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One:  Format of Internet Message
         Bodies", RFC 2045, November 1996.

   [5]   Freed, N., and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part Two:  Media Types", RFC 2046, November
         1996.

   [6]   Moore, K., "Multipurpose Internet Mail Extensions (MIME) Part
         Three:  Message Header Extensions for Non-Ascii Text", RFC
         2047, November 1996.

   [7]   Vaudreuil, G., "The Multipart/Report Content Type for the
         Reporting of Mail System Administrative Messages", RFC 1892,
         January 1996.

   [8]   Moore, K., "SMTP Service Extension for Delivery Status
         Notifications", RFC 1891, January 1996.

   [9]   Moore, K., and G. Vaudreuil, "An Extensible Format for
         Delivery Status Notifications, RFC 1894, January 1996.

   [10]  Bradner, S., "Key Words for Use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, March 1997.

13.  Author's Address

   Roger Fajman
   National Institutes of Health
   Building 12A, Room 3063
   12 South Drive MSC 5659
   Bethesda, Maryland 20892-5659
   USA

   EMail:  raf@cu.nih.gov
   Phone:  +1 301 402 4265
   Fax:    +1 301 480 6241

14.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 

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