Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-08
DMARC Working Group S. Jones, Ed.
Internet-Draft DMARC.org
Intended status: Informational K. Andersen
Expires: April 24, 2020 LinkedIn
October 22, 2019
Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-08
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 April 24, 2020.
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Jones & Andersen Expires April 24, 2020 [Page 1]
Internet-Draft ARC-USAGE October 2019
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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
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