Tunneling of SMTP Message Transfer Priorities
RFC 6758

Document Type RFC - Informational (October 2012; No errata)
Was draft-melnikov-smtp-priority-tunneling (individual in app area)
Last updated 2013-02-12
Stream IETF
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Stream WG state (None)
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IESG IESG state RFC 6758 (Informational)
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Responsible AD Pete Resnick
Send notices to alexey.melnikov@isode.com, carlberg@g11.org.uk, draft-melnikov-smtp-priority-tunneling@ietf.org
Internet Engineering Task Force (IETF)                       A. Melnikov
Request for Comments: 6758                                     Isode Ltd
Category: Informational                                      K. Carlberg
ISSN: 2070-1721                                                      G11
                                                            October 2012

             Tunneling of SMTP Message Transfer Priorities

Abstract

   This memo defines a mechanism for tunneling of SMTP (Simple Mail
   Transfer Protocol) Message Transfer Priority values through MTAs
   (Message Transfer Agents) that don't support the MT-PRIORITY SMTP
   extension.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6758.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Melnikov & Carlberg           Informational                     [Page 1]
RFC 6758        Tunneling of Message Transfer Priorities    October 2012

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................3
   3. Handling of Messages Received via SMTP ..........................4
      3.1. Handling of the MT-PRIORITY Parameter by the
           Receiving SMTP Server ......................................4
      3.2. Relay of Messages to Other Conforming SMTP/LMTP Servers ....4
      3.3. Relay of Messages to Non-Conforming SMTP/LMTP Servers ......5
      3.4. Mailing Lists and Aliases ..................................5
      3.5. Gatewaying a Message into a Foreign Environment ............5
      3.6. Interaction with the DSN SMTP Extension ....................5
   4. Header Field: MT-Priority .......................................5
   5. Example .........................................................6
   6. IANA Considerations .............................................7
   7. Security Considerations .........................................7
      7.1. Modification of the MT-Priority Header Field and DKIM ......9
   8. References ......................................................9
      8.1. Normative References .......................................9
      8.2. Informative References ....................................10
   Appendix A. Acknowledgements ......................................11

1.  Introduction

   The SMTP Message Transfer Priorities extension [RFC6710] specifies a
   mechanism to allow messages to be given a label to indicate
   preferential handling, to enable mail handling nodes to take this
   into account for onward processing.  However, as with all SMTP
   extensions, all SMTP Message Transfer Agents (MTAs) between the
   source and the destination must support the extension in order for it
   to be successfully used.  This document describes an application-
   layer tunneling of message priority, to convey the priority of the
   messages through MTAs that do not support the Message Transfer
   Priorities extension.  The tunneling is done by adding a new message
   header field to the Internet Message Format specified in [RFC5322].

   A number of other header fields are already in use, mostly in Message
   User Agents (MUAs), to convey meanings related to importance or
   priority of messages.  Examples of such header fields are Importance
   [RFC2156], Priority [RFC2156], and X-Priority (undocumented).
   Considering sometimes subtle and sometimes significant differences in
   the meaning of these header fields and widely different syntax, this
   document defines a new header field.
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