Message Submission for Mail
RFC 4409

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Network Working Group                                         R. Gellens
Request for Comments: 4409                                      QUALCOMM
Obsoletes: 2476                                               J. Klensin
Category: Standards Track                                     April 2006

                       Message Submission for Mail

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 (2006).

Abstract

   This memo splits message submission from message relay, allowing each
   service to operate according to its own rules (for security, policy,
   etc.), and specifies what actions are to be taken by a submission
   server.

   Message relay and final delivery are unaffected, and continue to use
   SMTP over port 25.

   When conforming to this document, message submission uses the
   protocol specified here, normally over port 587.

   This separation of function offers a number of benefits, including
   the ability to apply specific security or policy requirements.

Gellens & Klensin           Standards Track                     [Page 1]
RFC 4409              Message Submission for Mail             April 2006

Table of Contents

   1. Introduction ....................................................3
   2. Document Information ............................................4
      2.1. Definitions of Terms Used in This Memo .....................4
      2.2. Conventions Used in This Document ..........................5
   3. Message Submission ..............................................5
      3.1. Submission Identification ..................................5
      3.2. Message Rejection and Bouncing .............................5
      3.3. Authorized Submission ......................................6
   4. Mandatory Actions ...............................................7
      4.1. General Submission Rejection Code ..........................7
      4.2. Ensure All Domains Are Fully-Qualified .....................7
      4.3. Require Authentication .....................................8
   5. Recommended Actions .............................................8
      5.1. Enforce Address Syntax .....................................8
      5.2. Log Errors .................................................8
   6. Optional Actions ................................................9
      6.1. Enforce Submission Rights ..................................9
      6.2. Enforce Permissions ........................................9
      6.3. Check Message Data .........................................9
      6.4. Support for the Postmaster Address .........................9
   7. Interaction with SMTP Extensions ...............................10
   8. Message Modifications ..........................................11
      8.1. Add 'Sender' ..............................................11
      8.2. Add 'Date' ................................................11
      8.3. Add 'Message-ID' ..........................................11
      8.4. Transfer Encode ...........................................11
      8.5. Sign the Message ..........................................11
      8.6. Encrypt the Message .......................................12
      8.7. Resolve Aliases ...........................................12
      8.8. Header Rewriting ..........................................12
   9. Security Considerations ........................................12
   10. IANA Considerations ...........................................13
   11. Acknowledgements ..............................................13
   12. Normative References ..........................................14
   13. Informative References ........................................14

Gellens & Klensin           Standards Track                     [Page 2]
RFC 4409              Message Submission for Mail             April 2006

1.  Introduction

   SMTP was defined as a message *transfer* protocol, that is, a means
   to route (if needed) and deliver finished (complete) messages.

   Message Transfer Agents (MTAs) are not supposed to alter the message
   text, except to add 'Received', 'Return-Path', and other header
   fields as required by [SMTP-MTA].

   However, SMTP is now also widely used as a message *submission*
   protocol, that is, a means for Message User Agents (MUAs) to
   introduce new messages into the MTA routing network.  The process
   that accepts message submissions from MUAs is termed a Message
   Submission Agent (MSA).

   In order to permit unconstrained communications, SMTP is not often
   authenticated during message relay.