Domain-based Message Authentication, Reporting, and Conformance (DMARC) Failure Reporting
draft-ietf-dmarc-failure-reporting-01

DMARC Working Group                                     S. M. Jones, Ed.
Internet-Draft                                                 DMARC.org
Obsoletes: 7489 (if approved)                             A. Vesely, Ed.
Intended status: Standards Track                                    Tana
Expires: 22 August 2021                                 18 February 2021

Domain-based Message Authentication, Reporting, and Conformance (DMARC)
                           Failure Reporting
                 draft-ietf-dmarc-failure-reporting-01

Abstract

   Domain-based Message Authentication, Reporting, and Conformance
   (DMARC) is a scalable mechanism by which a domain owner can request
   feedback about email messages using their domain in the From: address
   field.  This document describes "failure reports," or "failed message
   reports," which provide details about individual messages that failed
   to authenticate according to the DMARC mechanism.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 22 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Failure Reports . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Reporting Format Update . . . . . . . . . . . . . . . . .   4
     3.2.  Verifying External Destinations . . . . . . . . . . . . .   5
     3.3.  Transport . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
     4.1.  Data Exposure Considerations  . . . . . . . . . . . . . .   5
     4.2.  Report Recipients . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   7
     A.1.  Entire Domain, Monitoring Only, Per-Message Reports . . .   8
     A.2.  Per-Message Failure Reports Directed to Third Party . . .   9
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Domain-based Message Authentication, Reporting, and Conformance
   (DMARC) [I-D.ietf-dmarc-dmarcbis] is a scalable mechanism by which a
   mail-originating organization can express domain-level policies and
   preferences for message validation, disposition, and reporting, that
   a mail-receiving organization can use to improve mail handling.  This
   document focuses on one type of reporting that can be requested under
   DMARC.

   Failure reports provide detailed information about the failure of a
   single message or a group of similar messages failing for the same
   reason.  They are meant to aid in cases where a domain owner is
   unable to detect why failures reported in aggregate form did occur.
   It is important to note these reports can contain either the header
   or the entire content of a failed message, which in turn may contain
   personally identifiable information, which should be considered when
   deciding whether to generate such reports.

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2.  Terminology and Definitions

   This section defines terms used in the rest of the document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Readers are expected to be familiar with the contents of
   [I-D.ietf-dmarc-dmarcbis], specifically the terminology and
   definitions section.

3.  Failure Reports

   Failure reports can supply more detailed information about messages
   that failed to authenticate, enabling the Domain Owner to determine
   exactly what might be causing those specific failures.

   Failure reports are normally generated and sent almost immediately
   after the Mail Receiver detects a DMARC failure.  Rather than waiting
   for an aggregate report, these reports are useful for quickly
   notifying the Domain Owners when there is an authentication failure.
   Whether the failure is due to an infrastructure problem or the
   message is inauthentic, failure reports also provide more information
   about the failed message than is available in an aggregate report.

   These reports should include as much of the message header and body
   as possible, consistent with the reporting party's privacy policies,
   to enable the Domain Owner to diagnose the authentication failure.

   When a Domain Owner requests failure reports for the purpose of
   forensic analysis, and the Mail Receiver is willing to provide such
   reports, the Mail Receiver generates and sends a message using the
   format described in [RFC6591]; this document updates that reporting
   format, as described in Section 3.1.

   The destination(s) and nature of the reports are defined by the "ruf"
   and "fo" tags as defined in Section 6.3 of [I-D.ietf-dmarc-dmarcbis].

   Where multiple URIs are selected to receive failure reports, the
   report generator MUST make an attempt to deliver to each of them.

   An obvious consideration is the denial-of-service attack that can be
   perpetrated by an attacker who sends numerous messages purporting to
   be from the intended victim Domain Owner but that fail both SPF and
   DKIM; this would cause participating Mail Receivers to send failure

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   reports to the Domain Owner or its delegate in potentially huge
   volumes.  Accordingly, participating Mail Receivers are encouraged to
   aggregate these reports as much as is practical, using the Incidents
   field of the Abuse Reporting Format ([RFC5965]).  Various aggregation
   techniques are possible, including the following:

   *  only send a report to the first recipient of multi-recipient
      messages;

   *  store reports for a period of time before sending them, allowing
      detection, collection, and reporting of like incidents;

   *  apply rate limiting, such as a maximum number of reports per
      minute that will be generated (and the remainder discarded).

3.1.  Reporting Format Update

   Operators implementing this specification also implement an augmented
   version of [RFC6591] as follows:

   1.  A DMARC failure report includes the following ARF header fields,
       with the indicated normative requirement levels:

       *  Identity-Alignment (REQUIRED; defined below)

       *  Delivery-Result (OPTIONAL)

       *  DKIM-Domain, DKIM-Identity, DKIM-Selector (REQUIRED if the
          message was signed by DKIM)

       *  DKIM-Canonicalized-Header, DKIM-Canonicalized-Body (OPTIONAL
          if the message was signed by DKIM)

       *  SPF-DNS (REQUIRED)

   2.  The "Identity-Alignment" field is defined to contain a comma-
       separated list of authentication mechanism names that produced an
       aligned identity, or the keyword "none" if none did.  ABNF:

     id-align     = "Identity-Alignment:" [CFWS]
                    ( "none" /
                      dmarc-method *( [CFWS] "," [CFWS] dmarc-method ) )
                    [CFWS]

     dmarc-method = ( "dkim" / "spf" )
                    ; each may appear at most once in an id-align

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   3.  Authentication Failure Type "dmarc" is defined, which is to be
       used when a failure report is generated because some or all of
       the authentication mechanisms failed to produce aligned
       identifiers.  Note that a failure report generator MAY also
       independently produce an AFRF message for any or all of the
       underlying authentication methods.

3.2.  Verifying External Destinations

   The procedure described for aggragate reports Section 2.1 of
   [I-D.ietf-dmarc-aggregate-reporting] applies to failure reports as
   well.

3.3.  Transport

   Email streams carrying DMARC failure reports SHOULD provide DMARC-
   based authentication, so as to produce "dmarc=pass".  This
   requirement is a MUST in case the report is sent through a host
   having a DMARC record with a ruf= tag.  Indeed, special care must be
   taken of authentication in that case, as failure to authenticate
   failure reports may result in mail loops.

   Reporters SHOULD rate limit the number of failure reports sent to any
   recipient to avoid overloading recipient systems.  Again, in case the
   reports being sent are in turn at risk of being reported for DMARC
   authentication failure, reporters MUST make sure that possible mail
   loop are stopped.

4.  Privacy Considerations

   This section discusses issues specific to private data that may be
   included in the DMARC reporting functions.

4.1.  Data Exposure Considerations

   Failed-message reporting provides message-specific details pertaining
   to authentication failures.  Individual reports can contain message
   content as well as trace header fields.  Domain Owners are able to
   analyze individual reports and attempt to determine root causes of
   authentication mechanism failures, gain insight into
   misconfigurations or other problems with email and network
   infrastructure, or inspect messages for insight into abusive
   practices.

   These reports may expose sender and recipient identifiers (e.g.,
   RFC5322.From addresses), and although the [RFC6591] format used for
   failed-message reporting supports redaction, failed-message reporting
   is capable of exposing the entire message to the report recipient.

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   Domain Owners requesting reports will receive information about mail
   claiming to be from them, which includes mail that was not, in fact,
   from them.  Information about the final destination of mail where it
   might otherwise be obscured by intermediate systems will therefore be
   exposed.

   When message-forwarding arrangements exist, Domain Owners requesting
   reports will also receive information about mail forwarded to domains
   that were not originally part of their messages' recipient lists.
   This means that destination domains previously unknown to the Domain
   Owner may now become visible.

   Disclosure of information about the messages is being requested by
   the entity generating the email in the first place, i.e., the Domain
   Owner and not the Mail Receiver, so this may not fit squarely within
   existing privacy policy provisions.  For some providers, failed-
   message reporting is viewed as a function similar to complaint
   reporting about spamming or phishing and is treated similarly under
   the privacy policy.  Report generators (i.e., Mail Receivers) are
   encouraged to review their reporting limitations under such policies
   before enabling DMARC reporting.

4.2.  Report Recipients

   A DMARC record can specify that reports should be sent to an
   intermediary operating on behalf of the Domain Owner.  This is done
   when the Domain Owner contracts with an entity to monitor mail
   streams for abuse and performance issues.  Receipt by third parties
   of such data may or may not be permitted by the Mail Receiver's
   privacy policy, terms of use, or other similar governing document.
   Domain Owners and Mail Receivers should both review and understand if
   their own internal policies constrain the use and transmission of
   DMARC reporting.

   Some potential exists for report recipients to perform traffic
   analysis, making it possible to obtain metadata about the Receiver's
   traffic.  In addition to verifying compliance with policies,
   Receivers need to consider that before sending reports to a third
   party.

5.  Security Considerations

   Considerations discussed in Section 11 of [I-D.ietf-dmarc-dmarcbis]
   apply.

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   In addition, note that Organizational Domains are only an
   approximation to actual domain ownership.  Therefore, reports may be
   sent to someone unrelated to the actual sender or domain owner.  That
   makes considerations in Section 4.1 all the more relevant.

6.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6591]  Fontana, H., "Authentication Failure Reporting Using the
              Abuse Reporting Format", RFC 6591, DOI 10.17487/RFC6591,
              April 2012, <https://www.rfc-editor.org/info/rfc6591>.

   [I-D.ietf-dmarc-dmarcbis]
              Gustafsson, E., Herr, T., and J. Levine, "Domain-based
              Message Authentication, Reporting, and Conformance
              (DMARC)", Work in Progress, Internet-Draft, draft-ietf-
              dmarc-dmarcbis-00, 11 November 2020,
              <https://tools.ietf.org/html/draft-ietf-dmarc-dmarcbis-
              00>.

   [I-D.ietf-dmarc-aggregate-reporting]
              Brotman, A., "DMARC Aggregate Reporting", Work in
              Progress, Internet-Draft, draft-ietf-dmarc-aggregate-
              reporting-00, 12 November 2020,
              <https://tools.ietf.org/html/draft-ietf-dmarc-aggregate-
              reporting-00>.

7.  Informative References

   [RFC5965]  Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              DOI 10.17487/RFC5965, August 2010,
              <https://www.rfc-editor.org/info/rfc5965>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Appendix A.  Examples

   This section presents some examples related to the use of DMARC
   reporting functions.

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A.1.  Entire Domain, Monitoring Only, Per-Message Reports

   The owners of the domain "example.com" have deployed SPF and DKIM on
   their messaging infrastructure.  As described in, Appendix B.2.1 of
   [I-D.ietf-dmarc-aggregate-reporting] they have used the aggregate
   reporting to discover some messaging systems that had not yet
   implemented DKIM correctly.  However, they are still seeing periodic
   authentication failures.  In order to diagnose these intermittent
   problems, they wish to request per-message failure reports when
   authentication failures occur.

   Not all Receivers will honor such a request, but the Domain Owner
   feels that any reports it does receive will be helpful enough to
   justify publishing this record.  The default per-message report
   format ([RFC6591]) meets the Domain Owner's needs in this scenario.

   The Domain Owner accomplishes this by adding the following to its
   policy record:

   *  Per-message failure reports should be sent via email to the
      address "auth-reports@example.com" ("ruf=mailto:auth-
      reports@example.com")

   The updated DMARC policy record might look like this when retrieved
   using a common command-line tool (the output shown would appear on a
   single line but is wrapped here for publication):

     % dig +short TXT _dmarc.example.com.
     "v=DMARC1; p=none; rua=mailto:dmarc-feedback@example.com;
      ruf=mailto:auth-reports@example.com"

   To publish such a record, the DNS administrator for the Domain Owner
   might create an entry like the following in the appropriate zone file
   (following the conventional zone file format):

     ; DMARC record for the domain example.com

     _dmarc  IN TXT ( "v=DMARC1; p=none; "
                       "rua=mailto:dmarc-feedback@example.com; "
                       "ruf=mailto:auth-reports@example.com" )

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A.2.  Per-Message Failure Reports Directed to Third Party

   The Domain Owner from the previous example is maintaining the same
   policy but now wishes to have a third party receive and process the
   per-message failure reports.  Again, not all Receivers will honor
   this request, but those that do may implement additional checks to
   validate that the third party wishes to receive the failure reports
   for this domain.

   The Domain Owner needs to alter its policy record from Appendix A.1
   as follows:

   *  Per-message failure reports should be sent via email to the
      address "auth-reports@thirdparty.example.net" ("ruf=mailto:auth-
      reports@thirdparty.example.net")

   The DMARC policy record might look like this when retrieved using a
   common command-line tool (the output shown would appear on a single
   line but is wrapped here for publication):

     % dig +short TXT _dmarc.example.com.
     "v=DMARC1; p=none; rua=mailto:dmarc-feedback@example.com;
      ruf=mailto:auth-reports@thirdparty.example.net"

   To publish such a record, the DNS administrator for the Domain Owner
   might create an entry like the following in the appropriate zone file
   (following the conventional zone file format):

     ; DMARC record for the domain example.com

     _dmarc IN TXT ( "v=DMARC1; p=none; "
                     "rua=mailto:dmarc-feedback@example.com; "
                     "ruf=mailto:auth-reports@thirdparty.example.net" )

   Because the address used in the "ruf" tag is outside the
   Organizational Domain in which this record is published, conforming
   Receivers will implement additional checks as described in
   Section 3.2 of this document.  In order to pass these additional
   checks, the third party will need to publish an additional DNS record
   as follows:

   *  Given the DMARC record published by the Domain Owner at
      "_dmarc.example.com", the DNS administrator for the third party
      will need to publish a TXT resource record at
      "example.com._report._dmarc.thirdparty.example.net" with the value
      "v=DMARC1;".

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   The resulting DNS record might look like this when retrieved using a
   common command-line tool (the output shown would appear on a single
   line but is wrapped here for publication):

     % dig +short TXT example.com._report._dmarc.thirdparty.example.net
     "v=DMARC1;"

   To publish such a record, the DNS administrator for example.net might
   create an entry like the following in the appropriate zone file
   (following the conventional zone file format):

     ; zone file for thirdparty.example.net
     ; Accept DMARC failure reports on behalf of example.com

     example.com._report._dmarc   IN   TXT    "v=DMARC1;"

   Intermediaries and other third parties should refer to Section 3.2
   for the full details of this mechanism.

Appendix B.  Change Log

   [RFC Editor: Please remove this section prior to publication.]

   00 to 01
       *  Replace references to RFC7489 with references to I-D.ietf-
          dmarc-dmarcbis.

       *  Replace the 2nd paragraph in the Introduction with the text
          proposed by Ned for Ticket #55, which enjoys some consensus:
          https://mailarchive.ietf.org/arch/msg/dmarc/
          HptVyJ9SgrfxWRbeGwORagPrhCw

       *  Strike a spurious sentence about criticality of feedback,
          which was meant for feedback in general, not failure reports.
          In fact, failure reports are not critical to establishing and
          maintaining accurate authentication deployments.  Still
          attributable to Ticket #55.

       *  Remove the content of section "Verifying External
          Destinations" and refer to I-D.ietf-dmarc-aggregate-reporting.

       *  Remove the content of section "Security Considerations" and
          refer to I-D.ietf-dmarc-dmarcbis.

       *  Slightly tweak the wording of the example in Appendix A.1 so
          that it makes sense standing alone.

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       *  Remove the sentence containing "must include any URI(s)", as
          the issue arose https://mailarchive.ietf.org/arch/msg/dmarc/
          mFk0qiTCy8tzghRvcxus01W_Blw.

       *  Add paragraph in Security Considerations, noting that note
          that Organizational Domains are only an approximation...

       *  Add a Transport section, mentioning DMARC conformance and
          failure report mail loops (Ticket #28).

Acknowledgements

   DMARC and the draft version of this document submitted to the
   Independent Submission Editor were the result of lengthy efforts by
   an informal industry consortium: DMARC.org (see http://dmarc.org
   (http://dmarc.org)).  Participating companies included Agari,
   American Greetings, AOL, Bank of America, Cloudmark, Comcast,
   Facebook, Fidelity Investments, Google, JPMorgan Chase & Company,
   LinkedIn, Microsoft, Netease, PayPal, ReturnPath, The Trusted Domain
   Project, and Yahoo!.  Although the contributors and supporters are
   too numerous to mention, notable individual contributions were made
   by J.  Trent Adams, Michael Adkins, Monica Chew, Dave Crocker, Tim
   Draegen, Steve Jones, Franck Martin, Brett McDowell, and Paul Midgen.
   The contributors would also like to recognize the invaluable input
   and guidance that was provided early on by J.D.  Falk.

   Additional contributions within the IETF context were made by Kurt
   Anderson, Michael Jack Assels, Les Barstow, Anne Bennett, Jim Fenton,
   J.  Gomez, Mike Jones, Scott Kitterman, Eliot Lear, John Levine, S.
   Moonesamy, Rolf Sonneveld, Henry Timmes, and Stephen J.  Turnbull.

Authors' Addresses

   Steven M Jones (editor)
   DMARC.org

   Email: smj@dmarc.org

   Alessandro Vesely (editor)
   Tana

   Email: vesely@tana.it

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