DMARC.org

smj@dmarc.org

Tana

vesely@tana.it

Application DMARC Domain-based Message Authentication, Reporting, and Conformance (DMARC) is a 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.

Introduction RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING: The source for this draft is maintained in GitHub at: https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-failure-reporting Domain-based Message Authentication, Reporting, and Conformance (DMARC) is a 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. Their purpose is twofold. On the one hand they are meant to aid in cases where a Domain Owner wishes to determine the cause of failures that were part of aggregate reports (see ). On the other hand, they can allow the Domain Owner to quickly identify and address harmful messages involving direct domain abuse. It is important to note that these reports can contain the header fields or sometimes the entire content of a failed message, which may contain personally identifiable information (PII). The potential disclosure of PII should be considered when deciding whether to request failure reports as a Domain Owner, or what information to include or redact in failure reports when creating them as a Mail Receiver, or whether to create failure reports at all; see .

Terminology There are a number of terms defined in that are used within this document. Understanding those definitions will aid in reading this 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 when, and only when, they appear in all capitals, as shown here.

DMARC Failure Reports Besides the header fields or the entire contents of a failed message, failure reports supply details about transmission and DMARC authentication, which may aid the Domain Owner in determining the cause of an authentication failure. 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. Failure reports also provide more information about the failed message than is available in an aggregate report. This allows the failure report consumer to better determine whether the failure is of a message that the domain owner intended to authenticate or one for which use of its domain was not authorized. These reports should include as much of the message header fields 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 ; this document updates that reporting format, as described in . The destination(s) to which failure reports are sent, and options for when they will be sent, are defined by the "ruf" and "fo" tags as defined in . When multiple URIs are provided to receive failure reports, the report generator MUST make an attempt to deliver to each of them. External destinations MUST be verified, see . Report generators MUST NOT consider "ruf" tags in DMARC Policy Records having a "psd=y" tag, unless there are specific agreements between the interested parties. Failure reports represent a possible denial-of-service attack that could be perpetrated by an attacker who sends numerous messages purporting to be from the intended victim Domain Owner but which fail both SPF and DKIM; this would cause participating Mail Receivers to send failure reports to the Domain Owner or its delegate(s), potentially in large numbers. Accordingly, participating Mail Receivers are encouraged to aggregate these reports as much as is practical, using the Incidents field of the Abuse Reporting Format . Indeed, the aim is not to count each and every failure, but rather to report different failure conditions. Various pruning techniques are possible, including the following:

• store reports for a period of time before sending them, allowing detection, collection, and consolidation of like incidents;
• apply rate limiting, such as a maximum number of reports per minute that will be generated (and the remainder discarded.)

Other Failure Reports This document describes only DMARC failure reports. DKIM failure reports and SPF failure reports are described in . A Mail Receiver generating DMARC failure reports MAY issue failure reports specific to the failed authentication mechanism instead of, or in addition to, DMARC failure reports, based on its own policy, the failure in question, and the content of the "fo" tag in the retrieved DMARC Policy Record. Note that DKIM failure reports and SPF failure reports can also be requested using the methods described in and respectively. Report Generators are free to follow any of the specifications.

Reporting Format Update Operators implementing this specification also implement an augmented version of 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 for DKIM failures of an aligned identifier)
   • DKIM-Canonicalized-Header, DKIM-Canonicalized-Body (OPTIONAL if reporting a DKIM failure)
   • SPF-DNS (REQUIRED for SPF failure of an aligned identifier)
2. The "Identity-Alignment" field is defined to contain a comma- separated list of authentication mechanism names that failed to authenticate 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

3. Authentication Failure Type "dmarc" is defined for the Auth-Failure field, 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 ARF message for any or all of the underlying authentication methods.

Verifying External Destinations It is possible to specify destinations for failure reports that are outside of the Organizational Domain of the DMARC Policy Record that was requesting the reports. These destinations are commonly referred to as "external destinations" and may represent a different domain controlled by the same organization, a contracted report processing service, or some other arrangement. Without this check, a bad actor could publish a DMARC Policy Record that requests that failure reports be sent to an external destination, then deliberately send messages that will generate failure reports as a form of abuse. Or, a Domain Owner could incorrectly publish a DMARC Policy Record with an external destination for failure reports, forcing the external destination to deal with unwanted messages and potential privacy issues. Therefore, in case of external destinations, a Mail Receiver who generates failure reports MUST use the Verifying External Destinations procedure described in , substituting the "ruf" tag where the "rua" tag appears in that procedure.`

Transport Email streams carrying DMARC failure reports SHOULD be DMARC aligned. Reporters MAY rate limit the number of failure reports sent to any recipient to avoid overloading recipient systems. Unaligned reports may in turn produce subsequent failure reports that could cause mail loops.

IANA Considerations

Feedback Report Header Fields Registry Update IANA is requested to change the "Identity-Alignment" entry in the "Feedback Report Header Fields" registry, which is part of ""Messaging Abuse Reporting Format" registry, to refer to this document.

Privacy Considerations The generation and transmission of DMARC failure reports raise significant privacy concerns that must be carefully considered before deployment. Given these factors, many large-scale providers limit or entirely disable the generation of failure reports, preferring to rely on aggregate reports, which provide statistical visibility without exposing sensitive content. Operators that choose to enable failure reporting are strongly encouraged to:

• Limit the scope and duration of use to targeted diagnostic activities.
• Ensure that reporting URIs are carefully controlled and validated.
• Apply minimization techniques, such as redaction of message bodies and header fields, to reduce sensitive data exposure.
• Always transmit reports over secure channels.

In summary, while DMARC failure reports can offer diagnostic value, the associated privacy concerns have led many operators to restrict their use. Aggregate reports remain the recommended mechanism for gaining visibility into authentication results while preserving the confidentiality of end-user communications. Particular privacy-specific issues are explored below.

Data Exposure Considerations Failure reports may include PII and non-public information (NPI) from messages that fail to authenticate, since these reports may contain message content as well as trace header fields. These reports may expose sender and recipient identifiers (e.g. RFC5322.From addresses), and although the format used for failed-message reporting supports redaction (), failed-message reporting is capable of exposing the entire message to the Report Consumer. They may also expose PII, sensitive business data, or other confidential communications to unintended recipients. Such exposure can create regulatory, legal, and operational risks for both senders and receivers. Examples include product launches, termination notices for employees, or calendar data. Even innocuous-seeming failures (such as malformed or "broken" calendar invitations) can result in the leakage of private communications. Domain Owners requesting reports will receive information about mail using their domain, but which they did not actually cause to be sent. This might provide valuable insight into content used in abusive messages, but it might also expose PII or NPI from legitimate messages mistakenly or accidentally failing authentication. Information about the final destination of mail, where it might otherwise be obscured by intermediate systems, may be exposed through a failure report. A commonly cited example is exposure of members of mailing lists when one list member sends messages to the list, and failure reports are generated when that message is delivered to other list members. Those failure reports would be sent to the Domain Owner of the list member posting the message, or their delegated Report Consumer(s). Similarly, when message forwarding arrangements exist, Domain Owners requesting reports may receive information about mail forwarded to domains that were not originally part of their messages' recipient list. This means that destinations previously unknown to the Domain Owner may now become visible.

Report Recipients A DMARC Policy Record can specify that reports should be sent to a Report Consumer operating on behalf of the Domain Owner. This might be done when the Domain Owner sends reports to an entity to monitor mail streams for deliverability, performance issues, or abuse. Receipt of such data by third parties may or may not be permitted by the Mail Receiver's privacy policy, terms of use, et cetera. Domain Owners and Mail Receivers should both review and understand whether their own internal policies constrain the use and transmission of DMARC reporting. Some potential exists for Report Consumers to perform traffic analysis, making it possible to obtain metadata about the Mail Receiver's traffic. In addition to verifying compliance with policies, Mail Receivers need to consider that before sending reports to a third party. On the other hand, a Domain Owner may publish a destination address that appears to be an Internal Report Consumer but is actually a forwarding address; in this case, the final destination of a report is not guaranteed.

Additional Damage The risks associated with failure reports are compounded by volume and content distribution concerns. Partially or unredacted reports may propagate large amounts of spam, phishing, or malware content, all of which may require special handling by Report Consumers or other recipients to avoid incidents. This underscores the need to avoid misconfiguration of the destinations in the "ruf" reporting URIs, and the suggestions for redaction in this document, for example using the method described in . And all of these concerns are heightened for high-volume domains. To mitigate such concerns, the following steps should be considered: By report generators:

• defang URIs by substituting hxxp for http;
• remove malicious attachments such as word documents or pdfs.

By report consumers:

• isolate report streams from other mail streams;
• use sandboxes in evaluating failure reports;
• use network segmentation;
• limit access to failure reports to authorized individuals with appropriate security training.

Security Considerations While reviewing this document and its Security Considerations, the reader should also review the Privacy Considerations above, as well as the Privacy Considerations and Security Considerations in sections and of ; and in sections and of .

Normative References Informative References

Example Failure Report This is the full content of a failure message, including the message header. Received: from gen.example (gen.example [192.0.2.1]) (TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by mail.consumer.example with ESMTPS id 00000000005DC0DD.0000442E; Tue, 19 Jul 2022 07:57:50 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gen.example; s=mail; t=1658210268; bh=rCrh1aFDE8d/Fltt8wbcu48bLOu4OM23QXqphUZPAIM=; h=From:To:Date:Subject:From; b=IND9JkuwF9/5841kzxMbPeej0VYimVzNKozR2R89M8eYO2zOlCBblx507Gz0YK7mE /h6pslWm0ODBVFzLlwY9CXv4Vu62QsN0RBIXHPjEXOkoM2VCD5zCd+5i5dtCFX7Mxh LThb2ZJ3efklbSB9RQRwxcmRvCPV7z6lt/Ds9sucVE1RDODYHjx+iWnAUQrlos6ZQb u/YOUGjf60LPpyljfPu3EpFwo80mSHyQlP/4S5KEykgPQMgCqLPPKvJwu1aAIDj+jG q2ylO3fmc/ERDeDWACtR67YNabEKBWtjqCRLNxKttazViJTZ5drcLfpX0853KoougX Rltp7zdoLdy4A== From: DMARC Filter <DMARC@gen.example>; To: dmarcfail@consumer.example Date: Tue, 19 Jul 2022 00:57:48 -0500 (CDT) Subject: FW: This is the original subject Mime-Version: 1.0 Content-Type: multipart/report; report-type=feedback-report; boundary="=_mime_boundary_" Message-Id: <20220719055748.4AE9D403CC@gen.example>; This is a MIME-formatted message. If you see this text it means that your E-mail software does not support MIME-formatted messages. --=_mime_boundary_ Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 7bit This is an authentication failure report for an email message received from IP 192.0.2.2 on Tue, 19 Jul 2022 00:57:48 -0500. --=_mime_boundary_ Content-Type: message/feedback-report Content-Transfer-Encoding: 7bit Feedback-Type: auth-failure Version: 1 User-Agent: DMARC-Filter/1.2.3 Auth-Failure: dmarc Authentication-Results: gen.example; dmarc=fail header.from=consumer.example Identity-Alignment: dkim DKIM-Domain: consumer.example DKIM-Identity: @consumer.example DKIM-Selector: epsilon Original-Envelope-Id: 65E1A3F0A0 Original-Mail-From: author=gen.example@forwarder.example Source-IP: 192.0.2.2 Source-Port: 12345 Reported-Domain: consumer.example --=_mime_boundary_ Content-Type: message/rfc822; charset=utf-8 Content-Transfer-Encoding: 7bit Authentication-Results: gen.example; dkim=permerror header.d=forwarder.example header.b="EjCbN/c3"; dkim=temperror header.d=forwarder.example header.b="mQ8GEWPc"; dkim=permerror header.d=consumer.example header.b="hETrymCb"; dkim=neutral header.d=consumer.example header.b="C2nsAp3A"; Received: from mail.forwarder.example (mail.forwarder.example [IPv6:2001:db8::23ac]) by mail.gen.example (Postfix) with ESMTP id 5E8B0C159826 for <x@gen.example>; Sun, 14 Aug 2022 07:58:29 -0700 (PDT) Received: from mail.forwarder.example (localhost [127.0.0.1]) by mail.forwarder.example (Postfix) with ESMTP id 4Ln7Qw4fnvz6Bq for <x@gen.example>; Tue, 19 Jul 2022 07:57:44 +0200 DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=forwarder.example; s=ed25519-59hs; t=1658210264; x=1663210264; bh=KYH/g7ForvDbnyyDLYSjauMYMW6sEIqu75/9w3OIONg=; h=Message-ID:Date:List-Id:List-Archive:List-Post:List-Help: List-Subscribe:List-Unsubscribe:List-Owner:MIME-Version:Subject: To:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding:autocrypt:cc:content-transfer-encoding: content-type:date:from:in-reply-to:message-id:mime-version: openpgp:references:subject:to; b=EjCbN/c3bTU4QkZH/zwTbYxBDp0k8kpmWSXh5h1M7T8J4vtRo+hvafJazT3ZRgq+7 +4dzEQwUhl+NOJYXXNUAA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=forwarder.example; s=rsa-wgJg; t=1658210264; x=1663210264; bh=KYH/g7ForvDbnyyDLYSjauMYMW6sEIqu75/9w3OIONg=; h=Message-ID:Date:List-Id:List-Archive:List-Post:List-Help: List-Subscribe:List-Unsubscribe:List-Owner:MIME-Version:Subject: To:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding:autocrypt:cc:content-transfer-encoding: content-type:date:from:in-reply-to:message-id:mime-version: openpgp:references:subject:to; b=mQ8GEWPcVpBpeqQ88pcbXpGHBT0J/Rwi8Zd2WZTXWWneQGRCOJLRcbBJpjqnrwtqd 76IqawH86tihz4Z/12J1GBCdNx1gfazsoI3yaqfooRDYg0mSyZHrYhQBmodnPcqZj4 /25L5278sc/UNrYO9az2n7R/skbVZ0bvSo2eEiGU8fcpO8+a5SKNYskhaviAI4eGIB iRMdEP7gP8dESdnZguNbY5HI32UMDpPPNqajzd/BgcqbveYpRrWCDOhcY47POV7GHM i/KLHiZXtJsL3/Pr/4TL+HTjdX8EDSsy1K5/JCvJCFsJHnSvkEaJQGLn/2m03eW9r8 9w1bQ90aY+VCQ== X-Original-To: users@forwarder.example Received: from mail.consumer.example (mail.consumer.example [192.0.2.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-384) server-digest SHA384) (Client did not present a certificate) by mail.forwarder.example (Postfix) with ESMTPS id 4Ln7Qs55xmz4nP for <users@forwarder.example>; Tue, 19 Jul 2022 07:57:41 +0200 (CEST) Authentication-Results: mail.forwarder.example; arc=none smtp.remote-ip=192.0.2.4 Authentication-Results: mail.forwarder.example; dkim=pass (512-bit key; secure) header.d=consumer.example header.i=@consumer.example header.a=ed25519-sha256 header.s=epsilon header.b=hETrymCb; dkim=pass (1152-bit key; secure) header.d=consumer.example header.i=@consumer.example header.a=rsa-sha256 header.s=delta header.b=C2nsAp3A DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=consumer.example; s=epsilon; t=1658210255; bh=KYH/g7ForvDbnyyDLYSjauMYMW6sEIqu75/9w3OIONg=; h=Date:Subject:To:References:From:In-Reply-To; b=hETrymCbz6T1Dyo5dCG9dk8rPykKLdhJCPFeJ9TiiP/kaoN2afpUYtj+SrI+I83lp p1F/FfYSGy7zz3Q3OdxBA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=consumer.example; s=delta; t=1658210255; bh=KYH/g7ForvDbnyyDLYSjauMYMW6sEIqu75/9w3OIONg=; h=Date:To:References:From:In-Reply-To; b=C2nsAp3AMNX33Nq7nN/StPo921xE3XGF8Ju3iAKdYB3EKhsril0N5IjWGlglJECst jLNKSo7KWZZ2lkH/dVZ9Rs1GHT2uaKy1sc/xmNIC5rHdhrxammiwpTSo4PsT8disfc 3DVF6Q62n0EsdLFqcw1KY8A9inFqYKY2tqoo+y4zMtItqCYx3xjsj3I0IFLuX Author: Message Author <author@consumer.example> Received: from [192.0.2.8] (host-8-2-0-192.isp.example [192.0.2.8]) (AUTH: CRAM-MD5 uXDGrn@SYT0/k, TLS: TLS1.3,128bits, ECDHE_RSA_AES_128_GCM_SHA256) by mail.consumer.example with ESMTPSA id 00000000005DC076.00004417; Tue, 19 Jul 2022 07:57:35 +0200 Message-ID: <2431dc66-b010-c9cc-4f2b-a1f889f8bdb4@consumer.example> Date: Tue, 19 Jul 2022 07:57:33 +0200 List-Id: <users.forwarder.example> List-Post: <mailto:users@forwarder.example> List-Help: <mailto:users+help@forwarder.example> List-Subscribe: <mailto:users+subscribe@forwarder.example> List-Unsubscribe: <mailto:users+unsubscribe@forwarder.example> List-Owner: <mailto:users+owner@forwarder.example> Precedence: list MIME-Version: 1.0 Subject: This is the original subject Content-Language: en-US To: users@forwarder.example Authentication-Results: consumer.example; auth=pass (details omitted) From: Message Author <author@consumer.example> In-Reply-To: <20220718102753.0f6d9dde.cel@example.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit [ Message body was here ] --=_mime_boundary_-- The Source-Port field definition is given by In the final MIME entity, the local-parts of To and From addresses are reported unredacted. Since we know that the local parts are PII, we can reduce the privacy risk by redacting them. In the example, the report generator could have replaced "users" with "lRLxexey" and "author" with "RT47aVey" throughout the entity. If the body of the message is not included, the last MIME entity would have "Content-Type: text/rfc822-headers" instead of message/rfc822.

Change Log {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.
• Remove the sentence containing "must include any URI(s)", as the issue arose <eref target="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).

01 to 02

• Add a sentence to make clear that counting failures is not the aim.

02 to 03

• Updated references.

03 to 04

• Add an example report.
• Remove the old Acknowledgements section.
• Add a IANA Consideration section

04 to 05

• Convert to markdown
• Remove irrelevant material.

05 to 06

• A Vesely was incorrectly removed from list of document editors. Corrected.
• Added Terminology section with recoomended boilerplate re: RFC2119.

06 to 07

• Reduce Terminology section
• minor nits

07 to 08

• Specify what detailed information a report contains, in the 1st paragraph of Section 2
• A couple of typos

08 to 09

• Replace &lt; with < and &gt; with > in Appendix B

09 to 10

• Add an informative section about other failure reports (DKIM, SPF)

10 to 11

• Remove appendix with redundant examples - pull request by Daniel K.

11 to 12

• Reference Terminology in
• Expand the Verifying External Destinations section and reference

12 to 13

• Update references to numbered sections of and
• Clarify potential information disclosures when failure reports are sent
• Minor edits for readability and clarity

13 to 14

• In the introduction (last paragraph) mention that the purpose is twofold, debug and anti-abuse.
• In Section 2 (2nd paragraph) clarify that failure reports allow better determining the failure reason.

14 to 15

• Expanded Privacy Considerations section as discussed on list.
• Add tentative IANA Consideration subsections.

15 to 16

• Qualification of RFCs 6651/2 in Section 3.
• Spell "Auth-Failure" at bullet 3 of Section 4.
• Cite RFC 6590 when mentioning redaction.
• s/using the wrong sending path/failing authentication/.
• Remove unnecessary IANA Considerations.

16 to 17

• Remove the last paragraph of Secority Considerations.

17 to 18

• Reword the first purpose (Intro) and cite aggregate-reporting.
• Forward reference to Privacy Consideration.
• s/fo=/"fo"/, /ruf=/ruf/, /urls/URIs/.
• Specify parent registry in IANA Considerations.

18 to 19

• Remove the term "scalable" from Abstract and Introduction.
• s/Sender Domain/Domain Owner/.
• Reference to dmarcbis, section 3.2 on its own line.
• Remove the phrase (sometimes referred to as "forensic reports").
• Note that Domain Owner can use dot-forward to not decalre consumer.
• Mention we could have encrypted the example.
• Don't mention MX.