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Network Working Group                                          E. AllmanRequest for Comments: 3886                                Sendmail, Inc.Updates:3463                                             September 2004Category: Standards TrackAn Extensible Message Format for Message Tracking ResponsesStatus 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 asRFC 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 20041.  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 asRFC 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].  Sections1.3   (Terminology), 2.1.1 (General conventions for DSN fields), 2.1.2   ("*-type" subfields), and 2.1.3 (Lexical tokens imported fromRFC822) 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 inRFC 2119 [RFC-   KEYWORDS].Allman                      Standards Track                     [Page 2]

RFC 3886                Message/Tracking-Status           September 20043.  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 insection 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 ofRFC 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 insection 3.2.  The per-   recipient fields are described insection 3.3.3.1.1.  General conventions for MTSN fieldsSection 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 20043.1.2.  *-type subfieldsSection 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 ofRFC 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 insection 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 insection 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 insection 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 inRFC 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 inRFC 3464.  A new code is added toRFC 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 20043.3.5.  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 Considerations4.1.  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 20044.2.  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 insection 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.  References7.1.  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,RFC1123, 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",RFC2822, 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",RFC2033, 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.COMAllman                      Standards Track                    [Page 10]

RFC 3886                Message/Tracking-Status           September 20049. Full Copyright Statement   Copyright (C) The Internet Society (2004).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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]