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rfc:rfc3886

Network Working Group E. Allman Request for Comments: 3886 Sendmail, Inc. Updates: 3463 September 2004 Category: Standards Track

    An Extensible Message Format for Message Tracking Responses

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 (2004).

Abstract

 Message Tracking is expected to be used to determine the status of
 undelivered e-mail upon request.  Tracking is used in conjunction
 with Delivery Status Notifications (DSN) and Message Disposition
 Notifications (MDN); generally, a message tracking request will be
 issued only when a DSN or MDN has not been received within a
 reasonable timeout period.
 This memo defines a MIME content-type for message tracking status in
 the same spirit as RFC 3464, "An Extensible Message Format for
 Delivery Status Notifications".  It is to be issued upon a request as
 described in "Message Tracking Query Protocol".  This memo defines
 only the format of the status information.  An extension to SMTP to
 label messages for further tracking and request tracking status is
 defined in a separate memo.

Allman Standards Track [Page 1] RFC 3886 Message/Tracking-Status September 2004

1. Introduction

 Message Tracking is expected to be used to determine the status of
 undelivered e-mail upon request.  Tracking is used in conjunction
 with Delivery Status Notifications (DSN) [RFC-DSN-SMTP] and Message
 Disposition Notifications (MDN) [RFC-MDN]; generally, a message
 tracking request will be issued only when a DSN or MDN has not been
 received within a reasonable timeout period.
 This memo defines a MIME [RFC-MIME] content-type for message tracking
 status in the same spirit as RFC 3464, "An Extensible Message Format
 for Delivery Status Notifications" [RFC-DSN-STAT].  It is to be
 issued upon a request as described in "Message Tracking Query
 Protocol" [RFC-MTRK-MTQP].  This memo defines only the format of the
 status information.  An extension to SMTP [RFC-ESMTP] to label
 messages for further tracking and request tracking status is defined
 in a separate memo [RFC-MTRK-SMTPEXT].

2. Other Documents and Conformance

 The model used for Message Tracking is described in [RFC-MTRK-MODEL].
 Message tracking is intended for use as a "last resort" mechanism.
 Normally, Delivery Status Notifications (DSNs) [RFC-DSN-SMTP] and
 Message Disposition Notifications (MDNs) [RFC-MDN] would provide the
 primary delivery status.  Only if no response is received from either
 of these mechanisms would Message Tracking be used.
 This document is based on [RFC-DSN-STAT].  Sections 1.3
 (Terminology), 2.1.1 (General conventions for DSN fields), 2.1.2
 ("*-type" subfields), and 2.1.3 (Lexical tokens imported from RFC
 822) of [RFC-DSN-STAT] are included into this document by reference.
 Other sections are further incorporated as described herein.
 Syntax notation in this document conforms to [RFC-ABNF].
 The following lexical tokens, defined in [RFC-MSGFMT], are used in
 the ABNF grammar for MTSNs: atom, CHAR, comment, CR, CRLF, DIGIT, LF,
 linear-white-space, SPACE, text.  The date-time lexical token is
 defined in [RFC-HOSTREQ].
 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 [RFC-
 KEYWORDS].

Allman Standards Track [Page 2] RFC 3886 Message/Tracking-Status September 2004

3. Format of a Message Tracking Status Notification

 A Message Tracking Status Notification (MTSN) is intended to be
 returned as the body of a Message Tracking request [RFC-MTRK-MTQP].
 The actual body MUST be a multipart/related [RFC-RELATED] with type
 parameter of "message/tracking-status"; each subpart MUST be of type
 "message/tracking-status" as described herein.  The multipart/related
 body can include multiple message/tracking-status parts if an MTQP
 server chains requests to the next server; see [RFC-MTRK-MODEL] and
 [RFC-MTRK-MTQP] for more information about chaining.

3.1. The message/tracking-status content-type

 The message/tracking-status content-type is defined as follows:
 MIME type name:           message
 MIME subtype name:        tracking-status
 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 4 of this memo.
 The body of a message/tracking-status is modeled after [RFC-DSN-
 STAT].  That body consists of one or more "fields" formatted to
 according to the ABNF of RFC 2822 header "fields" (see [RFC-MSGFMT]).
 The per-message fields appear first, followed by a blank line.
 Following the per-message fields are one or more groups of per-
 recipient fields.  Each group of per-recipient fields is preceded by
 a blank line.  Note that there will be a blank line between the final
 per-recipient field and the MIME boundary, since one CRLF is
 necessary to terminate the field, and a second is necessary to
 introduce the MIME boundary.  Formally, the syntax of the
 message/tracking-status content is as follows:
 tracking-status-content =
           per-message-fields 1*( CRLF per-recipient-fields )
 The per-message fields are described in section 3.2.  The per-
 recipient fields are described in section 3.3.

3.1.1. General conventions for MTSN fields

 Section 2.1.1 (General conventions for DSN fields) of [RFC-DSN-STAT]
 is included herein by reference.  Notably, the definition of xtext is
 identical to that of that document.

Allman Standards Track [Page 3] RFC 3886 Message/Tracking-Status September 2004

3.1.2. *-type subfields

 Section 2.1.2 (*-type subfields) of [RFC-DSN-STAT] is included herein
 by reference.  Notably, the definitions of address-type, diagnostic-
 type, and MTA-name type are identical to that of RFC 3464.

3.2. Per-Message MTSN Fields

 Some fields of an MTSN apply to all of the addresses in a single
 envelope.  These fields may appear at most once in any MTSN.  These
 fields are used to correlate the MTSN with the original message
 transaction and to provide additional information which may be useful
 to gateways.
    per-message-fields =
              original-envelope-id-field CRLF
              reporting-mta-field CRLF
              arrival-date-field CRLF
              *( extension-field CRLF )

3.2.1. The Original-Envelope-Id field

 The Original-Envelope-Id field is defined as in section 2.2.1 of
 [RFC-DSN-STAT].  This field is REQUIRED.

3.2.2. The Reporting-MTA field

 The Reporting-MTA field is defined as in section 2.2.2 of [RFC-DSN-
 STAT].  This field is REQUIRED.

3.2.3. The Arrival-Date field

 The Arrival-Date field is defined as in section 2.2.5 of [RFC-DSN-
 STAT].  This field is REQUIRED.

3.3. Per-Recipient MTSN fields

 An MTSN contains information about attempts to deliver a message to
 one or more recipients.  The delivery information for any particular
 recipient is contained in a group of contiguous per-recipient fields.
 Each group of per-recipient fields is preceded by a blank line.

Allman Standards Track [Page 4] RFC 3886 Message/Tracking-Status September 2004

 The syntax for the group of per-recipient fields is as follows:
    per-recipient-fields =
              original-recipient-field CRLF
              final-recipient-field CRLF
              action-field CRLF
              status-field CRLF
              [ remote-mta-field CRLF ]
              [ last-attempt-date-field CRLF ]
              [ will-retry-until-field CRLF ]
              *( extension-field CRLF )

3.3.1. Original-Recipient field

 The Original-Recipient field is defined as in section 2.3.1 of [RFC-
 DSN-STAT].  This field is REQUIRED.

3.3.2. Final-Recipient field

 The required Final-Recipient field is defined as in section 2.3.2 of
 [RFC-DSN-STAT].  This field is REQUIRED.

3.3.3. Action field

 The required Action field indicates the action performed by the
 Reporting-MTA as a result of its attempt to deliver the message to
 this recipient address.  This field MUST be present for each
 recipient named in the MTSN.  The syntax is as defined in RFC 3464.
 This field is REQUIRED.
 Valid actions are:
 failed       The message could not be delivered.  If DSNs have been
              enabled, a "failed" DSN should already have been
              returned.
 delayed      The message is currently waiting in the MTA queue for
              future delivery.  Essentially, this action means "the
              message is located, and it is here."
 delivered    The message has been successfully delivered to the final
              recipient.  This includes "delivery" to a mailing list
              exploder.  It does not indicate that the message has
              been read.  No further information is available; in
              particular, the tracking agent SHOULD NOT attempt
              further "downstream" tracking requests.

Allman Standards Track [Page 5] RFC 3886 Message/Tracking-Status September 2004

 expanded     The message has been successfully delivered to the
              recipient address as specified by the sender, and
              forwarded by the Reporting-MTA beyond that destination
              to multiple additional recipient addresses.  However,
              these additional addresses are not trackable, and the
              tracking agent SHOULD NOT attempt further "downstream"
              tracking requests.
 relayed      The message has been delivered into an environment that
              does not support message tracking.  No further
              information is available; in particular, the tracking
              agent SHOULD NOT attempt further "downstream" tracking
              requests.
 transferred  The message has been transferred to another MTRK-
              compliant MTA.  The tracking agent SHOULD attempt
              further "downstream" tracking requests unless that
              information is already given in a chaining response.
 opaque       The message may or may not have been seen by this
              system.  No further information is available or
              forthcoming.
 There may be some confusion between when to use "expanded" versus
 "delivered".  Whenever possible, "expanded" should be used when the
 MTA knows that the message will be sent to multiple addresses.
 However, in some cases the delivery occurs to a program which,
 unknown to the MTA, causes mailing list expansion; in the extreme
 case, the delivery may be to a real mailbox that has the side effect
 of list expansion.  If the MTA cannot ensure that this delivery will
 cause list expansion, it should set the action to "delivered".

3.3.4. Status field

 The Status field is defined as in RFC 3464.  A new code is added to
 RFC 3463 [RFC-EMSSC], "Enhanced Mail System Status Codes",
    X.1.9   Message relayed to non-compliant mailer"
       The mailbox address specified was valid, but the message has
       been relayed to a system that does not speak this protocol; no
       further information can be provided.
 A 2.1.9 Status field MUST be used exclusively with a "relayed" Action
 field.  This field is REQUIRED.

Allman Standards Track [Page 6] RFC 3886 Message/Tracking-Status September 2004

3.3.5. Remote-MTA field

 The Remote-MTA field is defined as in section Reference 2.3.5 of
 [RFC-DSN-STAT].  This field MUST NOT be included if no delivery
 attempts have been made or if the Action field has value "opaque".
 If delivery to some agent other than an MTA (for example, a Local
 Delivery Agent) then this field MAY be included, giving the name of
 the host on which that agent was contacted.

3.3.6. Last-Attempt-Date field

 The Last-Attempt-Date field is defined as in section Reference 2.3.7
 of [RFC-DSN-STAT].  This field is REQUIRED if any delivery attempt
 has been made and the Action field does not have value "opaque", in
 which case it will specify when it last attempted to deliver this
 message to another MTA or other Delivery Agent.  This field MUST NOT
 be included if no delivery attempts have been made.

3.3.7. Will-Retry-Until field

 The Will-Retry-Until field is defined as in section Reference 2.3.9
 of [RFC-DSN-STAT].  If the message is not in the local queue or the
 Action field has the value "opaque" the Will-Retry-Until field MUST
 NOT be included; otherwise, this field SHOULD be included.

3.4. Extension fields

 Future extension fields may be defined as defined in section 2.4 of
 [RFC-DSN-STAT].

3.5. Interaction Between MTAs and LDAs

 A message that has been delivered to a Local Delivery Agent (LDA)
 that understands message tracking (in particular, an LDA speaking
 LMTP [RFC-LMTP] that supports the MTRK extension) SHOULD pass the
 tracking request to the LDA.  In this case, the Action field for the
 MTA->LDA exchange will look the same as a transfer to a compliant
 MTA; that is, a "transferred" tracking status will be issued.

4. Security Considerations

4.1. Forgery

 Malicious servers may attempt to subvert message tracking and return
 false information.  This could result in misdirection or
 misinterpretation of results.

Allman Standards Track [Page 7] RFC 3886 Message/Tracking-Status September 2004

4.2. Confidentiality

 Another dimension of security is confidentiality.  There may be cases
 in which a message recipient is autoforwarding messages but does not
 wish to divulge the address to which the messages are autoforwarded.
 The desire for such confidentiality will probably be heightened as
 "wireless mailboxes", such as pagers, become more widely used as
 autoforward addresses.
 MTA authors are encouraged to provide a mechanism which enables the
 end user to preserve the confidentiality of a forwarding address.
 Depending on the degree of confidentiality required, and the nature
 of the environment to which a message were being forwarded, this
 might be accomplished by one or more of:
 (a)  respond with a "relayed" tracking status when a message is
      forwarded to a confidential forwarding address, and disabling
      further message tracking requests.
 (b)  declaring the message to be delivered, issuing a "delivered"
      tracking status, re-sending the message to the confidential
      forwarding address, and disabling further message tracking
      requests.
 The tracking algorithms MUST NOT allow tracking through list
 expansions.  When a message is delivered to a list, a tracking
 request MUST respond with an "expanded" tracking status and MUST NOT
 display the contents of the list.

5. IANA Considerations

 IANA has registered the SMTP extension defined in section 3.

6. Acknowledgements

 Several individuals have commented on and enhanced this document,
 including Tony Hansen, Philip Hazel, Alexey Melnikov, Lyndon
 Nerenberg, Chris Newman, Gregory Neil Shapiro, and Dan Wing.

7. References

7.1. Normative References

 [RFC-MTRK-MODEL]     Hansen, T., "Message Tracking Model and
                      Requirements", RFC 3888, September 2004.

Allman Standards Track [Page 8] RFC 3886 Message/Tracking-Status September 2004

 [RFC-MTRK-MTQP]      Hansen, T., "Message Tracking Query Protocol",
                      RFC 3887, September 2004.
 [RFC-MTRK-SMTPEXT]   Allman, E., "SMTP Service Extension for Message
                      Tracking", RFC 3885, September 2004.
 [RFC-ABNF]           Crocker, D., Ed. and P. Overell, "Augmented BNF
                      for Syntax Specifications: ABNF", RFC 2234,
                      November 1997.
 [RFC-EMSSC]          Vaudreuil, G., "Enhanced Mail System Status
                      Codes", RFC 3463, January 2003.
 [RFC-HOSTREQ]        Braden, R., Ed., "Requirements for Internet
                      Hosts -- Application and Support", STD 3, RFC
                      1123, October 1989.
 [RFC-KEYWORDS]       Bradner, S., "Key words for use in RFCs to
                      Indicate Requirement Levels", BCP 14, RFC 2119,
                      March 1997.
 [RFC-MIME]           Freed, N. and N. Borenstein, "Multipurpose
                      Internet Mail Extensions (MIME) Part One: Format
                      of Internet Message Bodies", RFC 2045, November
                      1996.
 [RFC-MSGFMT]         Resnick, P., Ed., "Internet Message Format", RFC
                      2822, April 2001.
 [RFC-RELATED]        Levinson, E., "The MIME Multipart/Related
                      Content-type", RFC 2387, August 1998.

7.2. Informational References

 [RFC-DSN-SMTP]       Moore, K., "Simple Mail Transfer Protocol (SMTP)
                      Service Extension for Delivery Status
                      Notifications (DSNs)", RFC 3461, January 2003.
 [RFC-DSN-STAT]       Moore, K. and G. Vaudreuil, "An Extensible
                      Message Format for Delivery Status
                      Notifications", RFC 3464, January 2003.
 [RFC-ESMTP]          Rose, M., Stefferud, E., Crocker, D., Klensin,
                      J., and N. Freed, "SMTP Service Extensions", STD
                      10, RFC 1869, November 1995.

Allman Standards Track [Page 9] RFC 3886 Message/Tracking-Status September 2004

 [RFC-LMTP]           Myers, J., "Local Mail Transfer Protocol", RFC
                      2033, October 1996.
 [RFC-MDN]            Hansen, T. and G. Vaudreuil, Eds., "Message
                      Disposition Notifications", RFC 3798, May 2004.

8. Author's Address

 Eric Allman
 Sendmail, Inc.
 6425 Christie Ave, 4th Floor
 Emeryville, CA  94608
 U.S.A.
 Phone: +1 510 594 5501
 Fax:   +1 510 594 5429
 EMail: eric@Sendmail.COM

Allman Standards Track [Page 10] RFC 3886 Message/Tracking-Status September 2004

9. Full Copyright Statement

 Copyright (C) The Internet Society (2004).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE
 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
 INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the IETF's procedures with respect to rights in IETF Documents can
 be found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at ietf-
 ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Allman Standards Track [Page 11]

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