Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-07

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DMARC Working Group                                        S. Jones, Ed.
Internet-Draft                                                 DMARC.org
Intended status: Informational                               K. Andersen
Expires: October 25, 2019                                       LinkedIn
                                                          April 23, 2019

      Recommended Usage of the Authenticated Received Chain (ARC)
                     draft-ietf-dmarc-arc-usage-07

Abstract

   The Authentication Received Chain (ARC) provides an authenticated
   "chain of custody" for a message, allowing each entity that handles
   the message to see what entities handled it before, and to see what
   the message's authentication assessment was at each step in the
   handling.  But the specification does not indicate how the entities
   handling these messages should interpret or utilize ARC results in
   making decisions about message disposition.  This document will
   provide guidance in these areas.

Status of This Memo

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   This Internet-Draft will expire on October 25, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   (https://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

Jones & Andersen        Expires October 25, 2019                [Page 1]
Internet-Draft                  ARC-USAGE                     April 2019

   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  How does ARC work?  . . . . . . . . . . . . . . . . . . .   3
     2.2.  What new headers are introduced by ARC? . . . . . . . . .   5
     2.3.  Does ARC support Internationalized Email (EAI)? . . . . .   5
     2.4.  Does ARC support multiple digital signature algorithms? .   5
   3.  Guidance for Receivers/Validators . . . . . . . . . . . . . .   5
     3.1.  What is the significance of an intact ARC chain?  . . . .   5
     3.2.  What exactly is an "intact" ARC chain?  . . . . . . . . .   6
     3.3.  What is the significance of an invalid ("broken") ARC
           chain?  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  What error code(s) should be returned if an invalid ARC
           chain is detected during an SMTP transaction? . . . . . .   7
     3.5.  What does the absence of an ARC chain in a message mean?    7
     3.6.  What reasonable conclusions can you draw based upon
           seeing lots of mail with ARC chains?  . . . . . . . . . .   7
     3.7.  What if none of the intermediaries have been seen
           previously? . . . . . . . . . . . . . . . . . . . . . . .   8
     3.8.  What about ARC chains where some intermediaries are known
           and others are not? . . . . . . . . . . . . . . . . . . .   8
     3.9.  What should message handlers do when they detect
           malicious content in messages where ARC is present? . . .   8
     3.10. What feedback does a sender or domain owner get about ARC
           when it is applied to their messages? . . . . . . . . . .   9
     3.11. What prevents a malicious actor from removing the ARC
           header fields, altering the content, and creating a new
           ARC chain?  . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Guidance for Intermediaries . . . . . . . . . . . . . . . . .   9
     4.1.  What is an Intermediary under ARC?  . . . . . . . . . . .   9
     4.2.  What are the minimum requirements for an ARC
           Intermediary? . . . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  More specifically a participating ARC intermediary
               must do the following:  . . . . . . . . . . . . . . .  10
     4.3.  Should every MTA be an ARC participant? . . . . . . . . .  10
     4.4.  What should an intermediary do in the case of an invalid