Interoperability Issues between Domain-based Message Authentication, Reporting, and Conformance (DMARC) and Indirect Email Flows
RFC 7960

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Internet Engineering Task Force (IETF)                    F. Martin, Ed.
Request for Comments: 7960                                      LinkedIn
Category: Informational                                     E. Lear, Ed.
ISSN: 2070-1721                                       Cisco Systems GmbH
                                                         T. Draegen, Ed.
                                                          dmarcian, inc.
                                                          E. Zwicky, Ed.
                                                                   Yahoo
                                                        K. Andersen, Ed.
                                                                LinkedIn
                                                          September 2016

  Interoperability Issues between Domain-based Message Authentication,
      Reporting, and Conformance (DMARC) and Indirect Email Flows

Abstract

   Domain-based Message Authentication, Reporting, and Conformance
   (DMARC) introduces a mechanism for expressing domain-level policies
   and preferences for email message validation, disposition, and
   reporting.  However, the DMARC mechanism enables potentially
   disruptive interoperability issues when messages do not flow directly
   from the author's administrative domain to the final Recipients.
   Collectively, these email flows are referred to as "indirect email
   flows".  This document describes these interoperability issues and
   presents possible methods for addressing them.

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 7841.

   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/rfc7960.

Martin, et al.                Informational                     [Page 1]
RFC 7960           DMARC Indirect Email Interop Issues    September 2016

Copyright Notice

   Copyright (c) 2016 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
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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.

Table of Contents

   1. Introduction ....................................................3
      1.1. Document Conventions .......................................4
   2. Causes of Interoperability Issues ...............................4
      2.1. Identifier Alignment .......................................4
           2.1.1. DKIM Identifier(s) ..................................5
           2.1.2. SPF Identifier(s) ...................................6
           2.1.3. Multiple RFC5322.From Addresses .....................6
      2.2. Message Forwarding .........................................6
      2.3. Message Modification .......................................7
   3. Internet Mail Architecture, DMARC, and Indirect Email Flows .....8
      3.1. Message Handling System ....................................8
           3.1.1. Message Submission Agents ...........................8
           3.1.2. Message Transfer Agents .............................9
                  3.1.2.1. Message Encoding ...........................9
                  3.1.2.2. Header Standardization ....................10
                  3.1.2.3. Content Validation ........................10
           3.1.3. Message Delivery Agents ............................10
      3.2. Mediators .................................................11
           3.2.1. Alias ..............................................11
           3.2.2. ReSenders ..........................................12
           3.2.3. Mailing Lists ......................................12
                  3.2.3.1. Mailing List Operational Effects ..........13
           3.2.4. Gateways ...........................................13
           3.2.5. Boundary Filters ...................................14
      3.3. Combinations ..............................................15
   4. Possible Mitigations of Interoperability Issues ................15