draft-ietf-dmarc-arc-usage-04.txt   draft-ietf-dmarc-arc-usage-05.txt 
DMARC Working Group S. Jones DMARC Working Group S. Jones
Internet-Draft DMARC.org Internet-Draft DMARC.org
Intended status: Informational K. Andersen Intended status: Informational K. Andersen
Expires: July 26, 2018 LinkedIn Expires: October 25, 2018 LinkedIn
J. Rae-Grant J. Rae-Grant
Google Google
T. Adams, Ed. T. Adams, Ed.
Paypal Paypal
January 22, 2018 April 23, 2018
Recommended Usage of the Authenticated Received Chain (ARC) Recommended Usage of the Authenticated Received Chain (ARC)
draft-ietf-dmarc-arc-usage-04 draft-ietf-dmarc-arc-usage-05
Abstract Abstract
The Authentication Received Chain (ARC) provides a means to preserve The Authentication Received Chain (ARC) provides a means to preserve
email authentication results and verify the identity of email message email authentication results and verify the identity of email message
handlers, each of which participates by inserting certain header handlers, each of which participates by inserting certain header
fields before passing the message on. But the specification does not fields before passing the message on. But the specification does not
indicate how intermediaries and receivers should interpret or utilize indicate how intermediaries and receivers should interpret or utilize
ARC. This document will provide guidance in these areas. ARC. This document will provide guidance in these areas.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 26, 2018. This Internet-Draft will expire on October 25, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. How does ARC work? . . . . . . . . . . . . . . . . . . . . . 3 2. How does ARC work? . . . . . . . . . . . . . . . . . . . . . 3
3. Guidance for Receivers/Validators . . . . . . . . . . . . . . 4 3. Guidance for Receivers/Validators . . . . . . . . . . . . . . 4
3.1. What is the significance of an intact ARC chain? . . . . 4 3.1. What is the significance of an intact ARC chain? . . . . 4
3.2. What exactly is an "intact" ARC chain? . . . . . . . . . 4 3.2. What exactly is an "intact" ARC chain? . . . . . . . . . 4
3.3. What is the significance of an invalid ("broken") ARC 3.3. What is the significance of an invalid ("broken") ARC
chain? . . . . . . . . . . . . . . . . . . . . . . . . . 5 chain? . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. What does the absence of an ARC chain in a message mean? 5 3.4. What does the absence of an ARC chain in a message mean? 5
3.5. What reasonable conclusions can you draw based upon 3.5. What reasonable conclusions can you draw based upon
seeing lots of mail with ARC chains? . . . . . . . . . . 5 seeing lots of mail with ARC chains? . . . . . . . . . . 6
3.6. What if none of the intermediaries have been seen 3.6. What if none of the intermediaries have been seen
previously? . . . . . . . . . . . . . . . . . . . . . . . 6 previously? . . . . . . . . . . . . . . . . . . . . . . . 6
3.7. What about ARC chains where some intermediaries are known 3.7. What about ARC chains where some intermediaries are known
and others are not? . . . . . . . . . . . . . . . . . . . 6 and others are not? . . . . . . . . . . . . . . . . . . . 6
3.8. What should message handlers do when they detect 3.8. What should message handlers do when they detect
malicious content in messages where ARC is present? . . . 6 malicious content in messages where ARC is present? . . . 7
3.9. What feedback does a sender or domain owner get about ARC 3.9. What feedback does a sender or domain owner get about ARC
when it is applied to their messages? . . . . . . . . . . 7 when it is applied to their messages? . . . . . . . . . . 7
3.10. What prevents a malicious actor from removing the ARC 3.10. What prevents a malicious actor from removing the ARC
header fields, altering the content, and creating a new header fields, altering the content, and creating a new
ARC chain? . . . . . . . . . . . . . . . . . . . . . . . 7 ARC chain? . . . . . . . . . . . . . . . . . . . . . . . 7
4. Guidance for Intermediaries . . . . . . . . . . . . . . . . . 8 4. Guidance for Intermediaries . . . . . . . . . . . . . . . . . 8
4.1. What is an Intermediary under ARC? . . . . . . . . . . . 8 4.1. What is an Intermediary under ARC? . . . . . . . . . . . 8
4.2. What are the minimum requirements for an ARC 4.2. What are the minimum requirements for an ARC
Intermediary? . . . . . . . . . . . . . . . . . . . . . . 8 Intermediary? . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. More specifically a participating ARC intermediary 4.2.1. More specifically a participating ARC intermediary
must do the following: . . . . . . . . . . . . . . . 8 must do the following: . . . . . . . . . . . . . . . 8
4.3. Should every MTA be an ARC participant? . . . . . . . . . 8 4.3. Should every MTA be an ARC participant? . . . . . . . . . 9
4.4. What should an intermediary do in the case of an invalid 4.4. What should an intermediary do in the case of an invalid
or "broken" ARC chain? . . . . . . . . . . . . . . . . . 9 or "broken" ARC chain? . . . . . . . . . . . . . . . . . 9
4.5. What should I do in the case where there is no ARC chain 4.5. What should I do in the case where there is no ARC chain
present in a message? . . . . . . . . . . . . . . . . . . 9 present in a message? . . . . . . . . . . . . . . . . . . 9
4.6. How could ARC affect my reputation as an intermediary? . 9 4.6. How could ARC affect my reputation as an intermediary? . 9
4.7. What can I do to influence my reputation as an 4.7. What can I do to influence my reputation as an
intermediary? . . . . . . . . . . . . . . . . . . . . . . 9 intermediary? . . . . . . . . . . . . . . . . . . . . . . 10
5. Guidance for Originators . . . . . . . . . . . . . . . . . . 10 5. Guidance for Originators . . . . . . . . . . . . . . . . . . 10
5.1. Where can I find out more information? . . . . . . . . . 10 5.1. Where can I find out more information? . . . . . . . . . 10
5.2. How/where can I test interoperabililty for my 5.2. How/where can I test interoperabililty for my
implementation? . . . . . . . . . . . . . . . . . . . . . 10 implementation? . . . . . . . . . . . . . . . . . . . . . 10
5.3. How can ARC impact my email? . . . . . . . . . . . . . . 10 5.3. How can ARC impact my email? . . . . . . . . . . . . . . 10
5.4. How can ARC impact my reputation as a message sender? . . 10 5.4. How can ARC impact my reputation as a message sender? . . 11
5.5. Can I tell intermediaries not to use ARC? . . . . . . . . 11 5.5. Can I tell intermediaries not to use ARC? . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . 11 6.1. Normative References . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . 11 6.2. Informative References . . . . . . . . . . . . . . . . . 12
6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix A. GLOSSARY . . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. GLOSSARY . . . . . . . . . . . . . . . . . . . . . . 12
Appendix B. References . . . . . . . . . . . . . . . . . . . . . 15 Appendix B. References . . . . . . . . . . . . . . . . . . . . . 15
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15
Appendix D. Comments and Feedback . . . . . . . . . . . . . . . 15 Appendix D. Comments and Feedback . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
[ARC] is intended to be used primarily by intermediaries, or message [ARC] is intended to be used primarily by intermediaries, or message
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reported by the first ARC intermediary that matches the domain in the reported by the first ARC intermediary that matches the domain in the
RFC5322.From header field, it will override a DMARC "p=reject" RFC5322.From header field, it will override a DMARC "p=reject"
policy. Another message receiver may decide to do so for intact ARC policy. Another message receiver may decide to do so for intact ARC
chains where the ARC-Authentication-Results header field indicates an chains where the ARC-Authentication-Results header field indicates an
SPF pass. A third message receiver may use very different criteria, SPF pass. A third message receiver may use very different criteria,
according to their requirements, while a fourth may choose not to according to their requirements, while a fourth may choose not to
take ARC information into account at all. take ARC information into account at all.
3.3. What is the significance of an invalid ("broken") ARC chain? 3.3. What is the significance of an invalid ("broken") ARC chain?
An ARC chain is not considered to be valid if the signatures in the An ARC chain is broken if the signatures in the ARC-Seal header
ARC-Seal header fields cannot be verified. For example the remote fields cannot be verified or if the most recent AMS can not be
server delivering the message to the local ADMD is not reflected in verified. For example the remote server delivering the message to
any ARC header fields, perhaps because they have not implemented ARC, the local ADMD is not reflected in any ARC header fields, perhaps
but they modified the message such that ARC and DKIM signatures because they have not implemented ARC, but they modified the message
already in the message were invalidated. such that ARC and DKIM signatures already in the message were
invalidated.
In such cases the ARC-Authentication-Results header field should not In case of a broken ARC chain, the message should be treated the same
have any influence on the disposition of the message. For example, a as if there was no ARC chain at all. For example, a message that
message that fails under DMARC and has an invalid ARC chain would be fails under DMARC and has an invalid ARC chain would be subject to
subject to that DMARC policy, which may cause it to be quarantined or that DMARC policy, which may cause it to be quarantined or rejected.
rejected.
Email transit can produce broken signatures for a wide variety of
benign reasons. This includes possibly breaking one or more ARC
signatures. Therefore, receivers need to be wary of ascribing motive
to such breakage although patterns of common behaviour may provide
some basis for adjusting local policy decisions.
3.4. What does the absence of an ARC chain in a message mean? 3.4. What does the absence of an ARC chain in a message mean?
The absence of an ARC chain means nothing. ARC is intended to allow The absence of an ARC chain means nothing. ARC is intended to allow
a participating message handler to preserve certain authentication a participating message handler to preserve certain authentication
results when a message is being forwarded and/or modified such that results when a message is being forwarded and/or modified such that
the final recipient can evaluate this information. If they are the final recipient can evaluate this information. If they are
absent, there is nothing extra that ARC requires the final recipient absent, there is nothing extra that ARC requires the final recipient
to do. to do.
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