Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-06

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DMARC Working Group                                        S. Jones, Ed.
Internet-Draft                                                 DMARC.org
Intended status: Informational                               K. Andersen
Expires: April 25, 2019                                         LinkedIn
                                                            J. Rae-Grant
                                                                  Google
                                                                T. Adams
                                                                  Paypal
                                                        October 22, 2018

      Recommended Usage of the Authenticated Received Chain (ARC)
                     draft-ietf-dmarc-arc-usage-06

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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Jones, et al.            Expires April 25, 2019                 [Page 1]
Internet-Draft                  ARC-USAGE                   October 2018

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  How does ARC work?  . . . . . . . . . . . . . . . . . . . . .   3
   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?  . . . . . . . . .   5
     3.3.  What is the significance of an invalid ("broken") ARC
           chain?  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  What does the absence of an ARC chain in a message mean?    6
     3.5.  What reasonable conclusions can you draw based upon
           seeing lots of mail with ARC chains?  . . . . . . . . . .   6
     3.6.  What if none of the intermediaries have been seen
           previously? . . . . . . . . . . . . . . . . . . . . . . .   7
     3.7.  What about ARC chains where some intermediaries are known
           and others are not? . . . . . . . . . . . . . . . . . . .   7
     3.8.  What should message handlers do when they detect
           malicious content in messages where ARC is present? . . .   7
     3.9.  What feedback does a sender or domain owner get about ARC
           when it is applied to their messages? . . . . . . . . . .   8
     3.10. What prevents a malicious actor from removing the ARC
           header fields, altering the content, and creating a new
           ARC chain?  . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Guidance for Intermediaries . . . . . . . . . . . . . . . . .   8
     4.1.  What is an Intermediary under ARC?  . . . . . . . . . . .   8
     4.2.  What are the minimum requirements for an ARC
           Intermediary? . . . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  More specifically a participating ARC intermediary
               must do the following:  . . . . . . . . . . . . . . .   9
     4.3.  Should every MTA be an ARC participant? . . . . . . . . .   9
     4.4.  What should an intermediary do in the case of an invalid
           or "broken" ARC chain?  . . . . . . . . . . . . . . . . .   9
     4.5.  What should I do in the case where there is no ARC chain