Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-03

Document Type Active Internet-Draft (dmarc WG)
Last updated 2017-12-19
Replaces draft-jones-arc-usage
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DMARC Working Group                                             S. Jones
Internet-Draft                                                 DMARC.org
Intended status: Informational                               K. Andersen
Expires: June 22, 2018                                          LinkedIn
                                                            J. Rae-Grant
                                                                  Google
                                                           T. Adams, Ed.
                                                                  Paypal
                                                       December 19, 2017

      Recommended Usage of the Authenticated Received Chain (ARC)
                     draft-ietf-dmarc-arc-usage-03

Abstract

   The Authentication Received Chain (ARC) provides a means to preserve
   email authentication results and verify the identity of email message
   handlers, each of which participates by inserting certain header
   fields before passing the message on.  But the specification does not
   indicate how intermediaries and receivers should interpret or utilize
   ARC.  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 June 22, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (https://trustee.ietf.org/license-info) in effect on the date of

Jones, et al.             Expires June 22, 2018                 [Page 1]
Internet-Draft                  ARC-USAGE                  December 2017

   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  How does ARC work?  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Evaluating the Efficacy of the ARC Protocol . . . . . . . . .   4
     3.1.  Success Consideration . . . . . . . . . . . . . . . . . .   4
     3.2.  Failure Considerations  . . . . . . . . . . . . . . . . .   5
     3.3.  Open Questions  . . . . . . . . . . . . . . . . . . . . .   5
       3.3.1.  Value of the ARC-Seal (AS) Header . . . . . . . . . .   5
       3.3.2.  DNS Overhead  . . . . . . . . . . . . . . . . . . . .   5
       3.3.3.  Distinguishing Valuable from Worthless Trace
               Information . . . . . . . . . . . . . . . . . . . . .   5
   4.  Guidance for Receivers/Validators . . . . . . . . . . . . . .   6
     4.1.  What is the significance of an intact ARC chain?  . . . .   6
     4.2.  What exactly is an "intact" ARC chain?  . . . . . . . . .   6
     4.3.  What is the significance of an invalid ("broken") ARC
           chain?  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  What does the absence of an ARC chain in a message mean?    7
     4.5.  What reasonable conclusions can you draw based upon
           seeing lots of mail with ARC chains?  . . . . . . . . . .   8
     4.6.  What if none of the intermediaries have been seen
           previously? . . . . . . . . . . . . . . . . . . . . . . .   8
     4.7.  What about ARC chains where some intermediaries are known
           and others are not? . . . . . . . . . . . . . . . . . . .   8
     4.8.  What should message handlers do when they detect
           malicious content in messages where ARC is present? . . .   9
     4.9.  What feedback does a sender or domain owner get about ARC
           when it is applied to their messages? . . . . . . . . . .   9
     4.10. What prevents a malicious actor from removing the ARC
           header fields, altering the content, and creating a new
           ARC chain?  . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Guidance for Intermediaries . . . . . . . . . . . . . . . . .  10
     5.1.  What is an Intermediary under ARC?  . . . . . . . . . . .  10
     5.2.  What are the minimum requirements for an ARC
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