draft-ietf-dmarc-dmarcbis-03.xml

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<rfc version="3" ipr="trust200902" docName="draft-ietf-dmarc-dmarcbis-03" submissionType="IETF" category="std" xml:lang="en" xmlns:xi="http://www.w3.org/2001/XInclude" obsoletes="7489" consensus="true">

<front>
<title abbrev="DMARCbis">Domain-based Message Authentication, Reporting, and Conformance (DMARC)</title><seriesInfo value="draft-ietf-dmarc-dmarcbis-03" stream="IETF" status="standard" name="Internet-Draft"></seriesInfo>
<author initials="T." surname="Herr (ed)" fullname="Todd M. Herr"><organization>Valimail</organization><address><postal><street></street>
</postal><email>todd.herr@valimail.com</email>
</address></author>
<author initials="J." surname="Levine (ed)" fullname="John Levine"><organization>Standcore LLC</organization><address><postal><street></street>
</postal><email>standards@standore.com</email>
</address></author>
<date/>
<area>Application</area>
<workgroup>DMARC</workgroup>

<abstract>
<t>This document describes the Domain-based Message Authentication,
Reporting, and Conformance (DMARC) protocol.</t>
<t>DMARC permits the owner of an email author's domain name to enable
verification of the domain's use, to indicate the Domain Owner's or
Public Suffix Operator's severity of concern regarding failed
verification, and to request reports about use of the domain name.
Mail receiving organizations can use this information when evaluating
handling choices for incoming mail.</t>
<t>This document obsoletes RFC 7489.</t>
</abstract>

</front>

<middle>

<section anchor="introduction"><name>Introduction</name>
<t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING:
The source for this draft is maintained in GitHub at:
<eref target="https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis">https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis</eref></t>
<t>Abusive email often includes unauthorized and deceptive use of a
domain name in the RFC5322.From header field. The domain typically
belongs to an organization expected to be known to - and presumably
trusted by - the recipient. The Sender Policy Framework (SPF) (<xref target="RFC7208"></xref>)
and DomainKeys Identified Mail (DKIM) (<xref target="RFC6376"></xref>) protocols provide
domain-level authentication but are not directly associated with the
RFC5322.From domain. DMARC leverages them, so that Domain Owners
publish a DNS record indicating their RFC5322.From field:</t>

<ul>
<li>Email authentication policies</li>
<li>Level of concern for mail that fails authentication checks</li>
<li>Desire for reports about email use of the domain name</li>
</ul>
<t>DMARC can cover non-existent sub-domains, below the &quot;Organizational
Domain&quot;, as well as domains at the top of the name hierarchy,
controlled by Public Suffix Operators (PSOs).</t>
<t>As with SPF and DKIM, DMARC classes results as &quot;pass&quot; or &quot;fail&quot;. A
pass from either SPF or DKIM is required. Depending on the stated
DMARC policy, the passed domain must be &quot;aligned&quot; with the RFC5322.From
domain in one of two modes - &quot;relaxed&quot; or &quot;strict&quot;.  Domains are said
to be &quot;in relaxed alignment&quot; if they have the same Organizational Domain,
which is at the top of the domain hierarchy, while having the same
administrative authority as the RFC5322.From domain, while domains are
&quot;in strict alignment&quot; if and only if they are identical.</t>
<t>A DMARC pass indicates only that the RFC5322.From domain has been
authenticated for that message; authentication does not carry an
explicit or implicit value assertion about that message or about
the Domain Owner. Indeed, a mail-receiving organization that performs
DMARC verification can choose to follow the Domain Owner's requested
disposition for authentication failures, and to inform the Domain
Owner of the mail handling decision for that message. It also might
choose different actions.</t>
<t>For a mail-receiving organization supporting DMARC, a message that
passes verification is part of a message stream that is reliably
associated with the RFC5322.From field Domain Owner. Therefore,
reputation assessment of that stream by the mail-receiving organization
is not encumbered by accounting for unauthorized use of that domain
in the RFC5322.From field.  A message that fails this verification
is not necessarily associated with the Domain Owner's domain and its
reputation.</t>
<t>DMARC, in the associated <xref target="DMARC-Aggregate-Reporting"></xref> and <xref target="DMARC-Failure-Reporting"></xref>
documents, also specifies a reporting framework. Using it, a mail-receiving
domain can generate regular reports about messages that claim to be from
a domain publishing DMARC policies, sending those reports to the address(es)
specified by the Domain Owner.</t>
<t>Use of DMARC creates some interoperability challenges that require due
consideration before deployment, particularly with configurations that
can cause mail to be rejected.  These are discussed in <xref target="other-topics"></xref>.</t>
</section>

<section anchor="requirements"><name>Requirements</name>
<t>Specification of DMARC is guided by the following high-level goals,
security dependencies, detailed requirements, and items that are
documented as out of scope.</t>

<section anchor="high-level-goals"><name>High-Level Goals</name>
<t>DMARC has the following high-level goals:</t>

<ul>
<li><t>Allow Domain Owners and PSOs to assert their severity of concern for
authentication failures for messages purporting to have
authorship within the domain.</t>
</li>
<li><t>Allow Domain Owners and PSOs to verify their authentication deployment.</t>
</li>
<li><t>Minimize implementation complexity for both senders and receivers,
as well as the impact on handling and delivery of legitimate
messages.</t>
</li>
<li><t>Reduce the amount of successfully delivered spoofed email.</t>
</li>
<li><t>Work at Internet scale.</t>
</li>
</ul>
</section>

<section anchor="out-of-scope"><name>Out of Scope</name>
<t>Several topics and issues are specifically out of scope for this
work.  These include the following:</t>

<ul>
<li><t>different treatment of messages that are not authenticated versus
those that fail authentication;</t>
</li>
<li><t>evaluation of anything other than RFC5322.From header field;</t>
</li>
<li><t>multiple reporting formats;</t>
</li>
<li><t>publishing policy other than via the DNS;</t>
</li>
<li><t>reporting or otherwise evaluating other than the last-hop IP
address;</t>
</li>
<li><t>attacks in the From: header field, also known as &quot;display name&quot;
attacks;</t>
</li>
<li><t>authentication of entities other than domains, since DMARC is
built upon SPF and DKIM, which authenticate domains; and</t>
</li>
<li><t>content analysis.</t>
</li>
</ul>
</section>

<section anchor="scalability"><name>Scalability</name>
<t>Scalability is a major issue for systems that need to operate in a
system as widely deployed as current SMTP email.  For this reason,
DMARC seeks to avoid the need for third parties or pre-sending
agreements between senders and receivers.  This preserves the
positive aspects of the current email infrastructure.</t>
<t>Although DMARC does not introduce third-party senders (namely
external agents authorized to send on behalf of an operator) to the
email-handling flow, it also does not preclude them.  Such third
parties are free to provide services in conjunction with DMARC.</t>
</section>

<section anchor="anti-phishing"><name>Anti-Phishing</name>
<t>DMARC is designed to prevent bad actors from sending mail that claims
to come from legitimate senders, particularly senders of
transactional email (official mail that is about business
transactions).  One of the primary uses of this kind of spoofed mail
is phishing (enticing users to provide information by pretending to
be the legitimate service requesting the information).  Thus, DMARC
is significantly informed by ongoing efforts to enact large-scale,
Internet-wide anti-phishing measures.</t>
<t>Although DMARC can only be used to combat specific forms of exact-
domain spoofing directly, the DMARC mechanism has been found to be
useful in the creation of reliable and defensible message streams.</t>
<t>DMARC does not attempt to solve all problems with spoofed or
otherwise fraudulent email.  In particular, it does not address the
use of visually similar domain names (&quot;cousin domains&quot;) or abuse of
the RFC5322.From human-readable &lt;display-name&gt;.</t>
</section>
</section>

<section anchor="terminology"><name>Terminology and Definitions</name>
<t>This section defines terms used in the rest of the document.</t>

<section anchor="conventions-used-in-this-document"><name>Conventions Used in This Document</name>
<t>The key words &quot;MUST&quot;, &quot;MUST NOT&quot;, &quot;REQUIRED&quot;, &quot;SHALL&quot;, &quot;SHALL NOT&quot;, &quot;SHOULD&quot;,
&quot;SHOULD NOT&quot;, &quot;RECOMMENDED&quot;, &quot;NOT RECOMMENDED&quot;, &quot;MAY&quot;, and &quot;OPTIONAL&quot; in this
document are to be interpreted as described in BCP 14 <xref target="RFC2119"></xref> <xref target="RFC8174"></xref>
when, and only when, they appear in all capitals, as shown here.</t>
<t>Readers are encouraged to be familiar with the contents of
<xref target="RFC5598"></xref>.  In particular, that document defines various roles in
the messaging infrastructure that can appear the same or separate in
various contexts.  For example, a Domain Owner could, via the
messaging security mechanisms on which DMARC is based, delegate the
ability to send mail as the Domain Owner to a third party with
another role.  This document does not address the distinctions among
such roles; the reader is encouraged to become familiar with that
material before continuing.</t>
</section>

<section anchor="authenticated-identifiers"><name>Authenticated Identifiers</name>
<t>Domain-level identifiers that are verified using authentication technologies
are referred to as &quot;Authenticated Identifiers&quot;.  See <xref target="authenication-mechanisms"></xref>
for details about the supported mechanisms.</t>
</section>

<section anchor="author-domain"><name>Author Domain</name>
<t>The domain name of the apparent author, as extracted from the From: header field.</t>
</section>

<section anchor="domain-owner"><name>Domain Owner</name>
<t>An entity or organization that owns a DNS domain.  The
term &quot;owns&quot; here indicates that the entity or organization being
referenced holds the registration of that DNS domain.  Domain
Owners range from complex, globally distributed organizations, to
service providers working on behalf of non-technical clients, to
individuals responsible for maintaining personal domains.  This
specification uses this term as analogous to an Administrative
Management Domain as defined in <xref target="RFC5598"></xref>.  It can also refer
to delegates, such as Report Receivers, when those are outside of
their immediate management domain.</t>
</section>

<section anchor="identifier-alignment"><name>Identifier Alignment</name>
<t>When the domain in the address in the From: header field has the
same Organizational Domain as a domain verified by SPF or DKIM
(or both), it has Identifier Alignment. (see below)</t>
</section>

<section anchor="longest-psd"><name>Longest PSD</name>
<t>The term Longest PSD is defined in <xref target="RFC9091"></xref>.</t>
</section>

<section anchor="mail-receiver"><name>Mail Receiver</name>
<t>The entity or organization that receives and processes email.<br />
Mail Receivers operate one or more Internet-facing Mail Transport
Agents (MTAs).</t>
</section>

<section anchor="non-existent-domains"><name>Non-existent Domains</name>
<t>For DMARC purposes, a non-existent domain is a domain for which there
is an NXDOMAIN or NODATA response for A, AAAA, and MX records.  This
is a broader definition than that in <xref target="RFC8020"></xref>.</t>
</section>

<section anchor="organizational-domain"><name>Organizational Domain</name>
<t>The domain that was registered with a domain name registrar.  In
the absence of more accurate methods, heuristics are used to determine
this, since it is not always the case that the registered domain name
is simply a top-level DNS domain plus one component (e.g., &quot;example.com&quot;,
where &quot;com&quot; is a top-level domain).  The Organizational Domain is
determined by applying the algorithm found in
<xref target="determining-the-organizational-domain"></xref>.</t>
</section>

<section anchor="public-suffix-domain"><name>Public Suffix Domain (PSD)</name>
<t>The term Public Suffix Domain is defined in <xref target="RFC9091"></xref>.</t>
</section>

<section anchor="public-suffix-operator"><name>Public Suffix Operator (PSO)</name>
<t>The term Public Suffix Operator is defined in <xref target="RFC9091"></xref>.</t>
</section>

<section anchor="pso-controlled-domain-names"><name>PSO Controlled Domain Names</name>
<t>The term PSO Controlled Domain Names is defined in <xref target="RFC9091"></xref>.</t>
</section>

<section anchor="report-receiver"><name>Report Receiver</name>
<t>An operator that receives reports from another operator
implementing the reporting mechanisms described in this document
and/or the documents <xref target="DMARC-Aggregate-Reporting"></xref> and <xref target="DMARC-Failure-Reporting"></xref>.
Such an operator might be receiving reports about messages related
to a domain for which it is the Domain Owner or PSO, or reports about
messages related to another operator's domain.  This term applies
collectively to the system components that receive and process these
reports and the organizations that operate them.</t>
</section>

<section anchor="more-on-identifier-alignment"><name>More on Identifier Alignment</name>
<t>Email authentication technologies authenticate various (and
disparate) aspects of an individual message.  For example, DKIM <xref target="RFC6376"></xref>
authenticates the domain that affixed a signature to the message,
while SPF <xref target="RFC7208"></xref> can authenticate either the domain that appears in the
RFC5321.MailFrom (MAIL FROM) portion of an SMTP <xref target="RFC5321"></xref> conversation or the
RFC5321.EHLO/HELO domain, or both.  These may be different domains, and they
are typically not visible to the end user.</t>
<t>DMARC authenticates use of the RFC5322.From domain by requiring that
it have the same Organizational Domain as (i.e., be aligned with) an
Authenticated Identifier. Domain names in this context are to be compared
in a case-insensitive manner, per <xref target="RFC4343"></xref>. The RFC5322.From domain
was selected as the central identity of the DMARC mechanism because it
is a required message header field and therefore guaranteed to be present
in compliant messages, and most Mail User Agents (MUAs) represent the
RFC5322.From header field as the originator of the message and render
some or all of this header field's content to end users.</t>
<t>It is important to note that Identifier Alignment cannot occur with a
message that is not valid per <xref target="RFC5322"></xref>, particularly one with a
malformed, absent, or repeated RFC5322.From header field, since in that case
there is no reliable way to determine a DMARC policy that applies to
the message.  Accordingly, DMARC operation is predicated on the input
being a valid RFC5322 message object, and handling of such
non-compliant cases is outside of the scope of this specification.
Further discussion of this can be found in <xref target="extract-author-domain"></xref>.</t>
<t>Each of the underlying authentication technologies that DMARC takes
as input yields authenticated domains as their outputs when they
succeed.</t>

<section anchor="dkim-identifiers"><name>DKIM-Authenticated Identifiers</name>
<t>DMARC requires Identifier Alignment based on the result of a DKIM
authentication because a message can bear a valid signature from any
domain, including domains used by a mailing list or even a bad actor.
Therefore, merely bearing a valid signature is not enough to infer
authenticity of the Author Domain.</t>
<t>DMARC permits Identifier Alignment based on the result of a DKIM
authentication to be strict or relaxed. (Note that these terms are
not related to DKIM's &quot;simple&quot; and &quot;relaxed&quot; canonicalization modes.)</t>
<t>In relaxed mode, the Organizational Domains of both the DKIM-authenticated
signing domain (taken from the value of the d= tag in the signature)
and that of the RFC5322.From domain must be equal if the identifiers
are to be considered to be aligned. In strict mode, only an exact match
between both Fully Qualified Domain Names (FQDNs) is considered to produce
Identifier Alignment.</t>
<t>To illustrate, in relaxed mode, if a verified DKIM signature
successfully verifies with a &quot;d=&quot; domain of &quot;example.com&quot;, and the
RFC5322.From address is &quot;alerts@news.example.com&quot;, the DKIM &quot;d=&quot;
domain and the RFC5322.From domain are considered to be &quot;in alignment&quot;,
because both domains have the same Organizational Domain of &quot;example.com&quot;.
In strict mode, this test would fail because the d= domain does not
exactly match the RFC5322.From domain.</t>
<t>However, a DKIM signature bearing a value of &quot;d=com&quot; would never allow
an &quot;in alignment&quot; result, as &quot;com&quot; should appear on all public suffix
lists (see <xref target="public-suffix-lists"></xref>) and therefore cannot be an Organizational
Domain.</t>
<t>Note that a single email can contain multiple DKIM signatures, and it
is considered to produce a DMARC &quot;pass&quot; result if any DKIM signature
is aligned and verifies.</t>
</section>

<section anchor="spf-identifiers"><name>SPF-Authenticated Identifiers</name>
<t>DMARC permits Identifier Alignment based on the result of an SPF
authentication. As with DKIM, Identifier Alignement can be either
strict or relaxed.</t>
<t>In relaxed mode, the Organizational Domains of the SPF-authenticated
domain and RFC5322.From domain must be equal if the identifiers are
to be considered to be aligned. In strict mode, the two FQDNs must
match exactly in order from them to be considered to be aligned.</t>
<t>For example, in relaxed mode, if a message passes an SPF check with an
RFC5321.MailFrom domain of &quot;cbg.bounces.example.com&quot;, and the address
portion of the RFC5322.From header field contains
&quot;payments@example.com&quot;, the Authenticated RFC5321.MailFrom domain
identifier and the RFC5322.From domain are considered to be &quot;in
alignment&quot; because they have the same Organizational Domain
(&quot;example.com&quot;). In strict mode, this test would fail because the
two domains are not identical.</t>
<t>The reader should note that SPF alignment checks in DMARC rely solely
on the RFC5321.MailFrom domain. This differs from section 2.3 of
<xref target="RFC7208"></xref>, which recommends that SPF checks be done on not only the
&quot;MAIL FROM&quot; but also on a separate check of the &quot;HELO&quot; identity.</t>
</section>

<section anchor="alignment-and-extension-technologies"><name>Alignment and Extension Technologies</name>
<t>If in the future DMARC is extended to include the use of other
authentication mechanisms, the extensions will need to allow for
domain identifier extraction so that alignment with the RFC5322.From
domain can be verified.</t>
</section>
</section>

<section anchor="determining-the-organizational-domain"><name>Determining The Organizational Domain</name>
<t>The Organizational Domain is determined using the following
algorithm:</t>

<ol>
<li><t>Acquire a &quot;public suffix&quot; list, i.e., a list of DNS domain names
reserved for registrations.  Some country Top-Level Domains
(TLDs) make specific registration requirements, e.g., the United
Kingdom places company registrations under &quot;.co.uk&quot;; other TLDs
such as &quot;.com&quot; appear in the IANA registry of top-level DNS
domains.  A public suffix list is the union of all of these.
<xref target="public-suffix-lists"></xref> contains some discussion about obtaining a public
suffix list.</t>
</li>
<li><t>Break the subject DNS domain name into a set of &quot;n&quot; ordered
labels.  Number these labels from right to left; e.g., for
&quot;example.com&quot;, &quot;com&quot; would be label 1 and &quot;example&quot; would be
label 2.</t>
</li>
<li><t>Search the public suffix list for the name that matches the
largest number of labels found in the subject DNS domain.  Let
that number be &quot;x&quot;.</t>
</li>
<li><t>Construct a new DNS domain name using the name that matched from
the public suffix list and prefixing to it the &quot;x+1&quot;th label from
the subject domain.  This new name is the Organizational Domain.</t>
</li>
</ol>
<t>Thus, since &quot;com&quot; is an IANA-registered TLD, a subject domain of
&quot;a.b.c.d.example.com&quot; would have an Organizational Domain of
&quot;example.com&quot;.</t>
<t>The process of determining a suffix is currently a heuristic one.  No
list is guaranteed to be accurate or current.</t>
</section>
</section>

<section anchor="overview"><name>Overview</name>
<t>This section provides a general overview of the design and operation
of the DMARC environment.</t>

<section anchor="authenication-mechanisms"><name>Authentication Mechanisms</name>
<t>The following mechanisms for determining Authenticated Identifiers
are supported in this version of DMARC:</t>

<ul>
<li><t>DKIM, <xref target="RFC6376"></xref>, which provides a domain-level identifier in the content of
the &quot;d=&quot; tag of a verified DKIM-Signature header field.</t>
</li>
<li><t>SPF, <xref target="RFC7208"></xref>, which can authenticate both the domain found in
an <xref target="RFC5321"></xref> HELO/EHLO command (the HELO identity) and the domain
found in an SMTP MAIL command (the MAIL FROM identity). As noted earlier,
however, DMARC relies solely on SPF authentication of the domain found in
SMTP MAIL FROM command. Section 2.4 of <xref target="RFC7208"></xref> describes MAIL FROM
processing for cases in which the MAIL command has a null path.</t>
</li>
</ul>
</section>

<section anchor="key-concepts"><name>Key Concepts</name>
<t>DMARC policies are published by the Domain Owner or PSO, and retrieved by
the Mail Receiver during the SMTP session, via the DNS.</t>
<t>DMARC's verification function is based on whether the RFC5322.From
domain is aligned with an authenticated domain name from SPF or DKIM.<br />
When a DMARC policy is published for the domain name found in the
RFC5322.From header field, and that domain name is not verified
through SPF or DKIM, the handling of that message can be affected
by that DMARC policy when delivered to a participating receiver.</t>
<t>It is important to note that the authentication mechanisms employed
by DMARC authenticate only a DNS domain and do not authenticate the
local-part of any email address identifier found in a message, nor do
they validate the legitimacy of message content.</t>
<t>DMARC's feedback component involves the collection of information
about received messages claiming to be from the Author Domain
for periodic aggregate reports to the Domain Owner or PSO.  The
parameters and format for such reports are discussed in <xref target="DMARC-Aggregate-Reporting"></xref></t>
<t>A DMARC-enabled Mail Receiver might also generate per-message reports
that contain information related to individual messages that fail SPF
and/or DKIM.  Per-message failure reports are a useful source of
information when debugging deployments (if messages can be determined
to be legitimate even though failing authentication) or in analyzing
attacks.  The capability for such services is enabled by DMARC but
defined in other referenced material such as <xref target="RFC6591"></xref> and <xref target="DMARC-Failure-Reporting"></xref></t>
<t>A message satisfies the DMARC checks if at least one of the supported
authentication mechanisms:</t>

<ol>
<li><t>produces a &quot;pass&quot; result, and</t>
</li>
<li><t>produces that result based on an identifier that is in alignment,
as defined in <xref target="terminology"></xref>.</t>
</li>
</ol>
</section>

<section anchor="flow-diagram"><name>Flow Diagram</name>

<sourcecode type="ascii-art"> +---------------+                             +--------------------+
 | Author Domain |&lt; . . . . . . . . . . . .    | Return-Path Domain |
 +---------------+                        .    +--------------------+
     |                                    .               ^
     V                                    V               .
 +-----------+     +--------+       +----------+          v
 |   MSA     |&lt;***&gt;|  DKIM  |       |   DMARC  |     +----------+
 |  Service  |     | Signer |       | Verifier |&lt;***&gt;|    SPF   |
 +-----------+     +--------+       +----------+  *  | Verifier |
     |                                    ^       *  +----------+
     |                                    *       *
     V                                    v       *
  +------+        (~~~~~~~~~~~~)      +------+    *  +----------+
  | sMTA |-------&gt;( other MTAs )-----&gt;| rMTA |    **&gt;|   DKIM   |
  +------+        (~~~~~~~~~~~~)      +------+       | Verifier |
                                         |           +----------+
                                         |                ^
                                         V                .
                                  +-----------+           .
                    +---------+   |    MDA    |           v
                    |  User   |&lt;--| Filtering |      +-----------+
                    | Mailbox |   |  Engine   |      |   DKIM    |
                    +---------+   +-----------+      |  Signing  |
                                                     | Domain(s) |
                                                     +-----------+

  MSA = Mail Submission Agent
  MDA = Mail Delivery Agent
</sourcecode>
<t>The above diagram shows a simple flow of messages through a DMARC-
aware system.  Solid lines denote the actual message flow, dotted
lines involve DNS queries used to retrieve message policy related to
the supported message authentication schemes, and asterisk lines
indicate data exchange between message-handling modules and message
authentication modules.  &quot;sMTA&quot; is the sending MTA, and &quot;rMTA&quot; is the
receiving MTA.</t>
<t>Put simply, when a message reaches a DMARC-aware rMTA, a DNS query
will be initiated to determine if the author domain has published
a DMARC policy. If a policy is found, the rMTA will use the results
of SPF and DKIM verification checks to determine the ultimate DMARC
authentication status. The DMARC status can then factor into the
message handling decision made by the recipient's mail sytsem.</t>
<t>More details on specific actions for the parties involved can be
found in <xref target="domain-owner-actions"></xref> and <xref target="mail-receiver-actions"></xref>.</t>
</section>
</section>

<section anchor="use-of-rfc5322-from"><name>Use of RFC5322.From</name>
<t>One of the most obvious points of security scrutiny for DMARC is the
choice to focus on an identifier, namely the RFC5322.From address,
which is part of a body of data that has been trivially forged
throughout the history of email. This field is the one used by end
users to identify the source of the message, and so it has always
been a prime target for abuse through such forgery and other means.</t>
<t>Several points suggest that it is the most correct and safest thing
to do in this context:</t>

<ul>
<li><t>Of all the identifiers that are part of the message itself, this
is the only one guaranteed to be present.</t>
</li>
<li><t>It seems the best choice of an identifier on which to focus, as
most MUAs display some or all of the contents of that field in a
manner strongly suggesting those data as reflective of the true
originator of the message.</t>
</li>
<li><t>Many high-profile email sources, such as email service providers,
require that the sending agent have authenticated before email
can be generated.  Thus, for these mailboxes, the mechanism
described in this document provides recipient end users with strong
evidence that the message was indeed originated by the agent they
associate with that mailbox, if the end user knows that these
various protections have been provided.</t>
</li>
</ul>
<t>The absence of a single, properly formed RFC5322.From header field renders
the message invalid.  Handling of such a message is outside of the
scope of this specification.</t>
<t>Since the sorts of mail typically protected by DMARC participants
tend to only have single Authors, DMARC participants generally
operate under a slightly restricted profile of RFC5322 with respect
to the expected syntax of this field.  See <xref target="mail-receiver-actions"></xref>
for details.</t>
</section>

<section anchor="policy"><name>Policy</name>
<t>DMARC policies are published by Domain Owners and PSOs and can be
used by Mail Receivers to inform their message handling decisions.</t>
<t>A Domain Owner or PSO advertises DMARC participation of one or more of its
domains by adding a DNS TXT record (described in <xref target="dmarc-policy-record"></xref>) to
those domains.  In doing so, Domain Owners and PSOs indicate their severity of
concern regarding failed authentication for email messages making use
of their domain in the RFC5322.From header field as well as the provision
of feedback about those messages. Mail Receivers in turn can take into
account the Domain Owner's severity of concern when making handling
decisions about email messages that fail DMARC authentication checks.</t>
<t>A Domain Owner or PSO may choose not to participate in DMARC evaluation by
Mail Receivers.  In this case, the Domain Owner simply declines to
advertise participation in those schemes.  For example, if the
results of path authorization checks ought not be considered as part
of the overall DMARC result for a given Author Domain, then the
Domain Owner does not publish an SPF policy record that can produce
an SPF pass result.</t>
<t>A Mail Receiver implementing the DMARC mechanism SHOULD make a
best-effort attempt to adhere to the Domain Owner's or PSO's published DMARC
Domain Owner Assessment Policy when a message fails the DMARC test.<br />
Since email streams can be complicated (due to forwarding, existing RFC5322.From
domain-spoofing services, etc.), Mail Receivers MAY deviate from a published
Domain Owner Assessment Policy during message processing and SHOULD
make available the fact of and reason for the deviation to the Domain
Owner via feedback reporting, specifically using the &quot;PolicyOverride&quot;
feature of the aggregate report defined in <xref target="DMARC-Aggregate-Reporting"></xref></t>

<section anchor="dmarc-policy-record"><name>DMARC Policy Record</name>
<t>Domain Owner and PSO DMARC preferences are stored as DNS TXT records in
subdomains named &quot;_dmarc&quot;.  For example, the Domain Owner of
&quot;example.com&quot; would post DMARC preferences in a TXT record at
&quot;_dmarc.example.com&quot;.  Similarly, a Mail Receiver wishing to query
for DMARC preferences regarding mail with an RFC5322.From domain of
&quot;example.com&quot; would issue a TXT query to the DNS for the subdomain of
&quot;_dmarc.example.com&quot;.  The DNS-located DMARC preference data will
hereafter be called the &quot;DMARC record&quot;.</t>
<t>DMARC's use of the Domain Name Service is driven by DMARC's use of
domain names and the nature of the query it performs.  The query
requirement matches with the DNS, for obtaining simple parametric
information.  It uses an established method of storing the
information, associated with the target domain name, namely an
isolated TXT record that is restricted to the DMARC context.  Use of
the DNS as the query service has the benefit of reusing an extremely
well-established operations, administration, and management
infrastructure, rather than creating a new one.</t>
<t>Per <xref target="RFC1035"></xref>, a TXT record can comprise several &quot;character-string&quot;
objects.  Where this is the case, the module performing DMARC
evaluation MUST concatenate these strings by joining together the
objects in order and parsing the result as a single string.</t>
</section>

<section anchor="dmarc-uris"><name>DMARC URIs</name>
<t><xref target="RFC3986"></xref> defines a generic syntax for identifying a resource.  The DMARC
mechanism uses this as the format by which a Domain Owner or PSO specifies
the destination for the two report types that are supported.</t>
<t>The place such URIs are specified (see <xref target="general-record-format"></xref>) allows
a list of these to be provided.  The list of URIs is separated by commas
(ASCII 0x2c).  A report SHOULD be sent to each listed URI provided in
the DMARC record.</t>
<t>A formal definition is provided in <xref target="formal-definition"></xref>.</t>
</section>

<section anchor="general-record-format"><name>General Record Format</name>
<t>DMARC records follow the extensible &quot;tag-value&quot; syntax for DNS-based
key records defined in DKIM <xref target="RFC6376"></xref>.</t>
<t><xref target="iana-considerations"></xref> creates a registry for known DMARC tags and
registers the initial set defined in this document.  Only tags defined
in this document or in later extensions, and thus added to that registry,
are to be processed; unknown tags MUST be ignored.</t>
<t>The following tags are valid DMARC tags:</t>

<dl>
<dt>adkim:</dt>
<dd><t>(plain-text; OPTIONAL; default is &quot;r&quot;.)  Indicates whether
strict or relaxed DKIM Identifier Alignment mode is required by
the Domain Owner.  See <xref target="dkim-identifiers"></xref> for details.  Valid values
are as follows:</t>

<dl>
<dt>r:</dt>
<dd>relaxed mode</dd>
<dt>s:</dt>
<dd>strict mode</dd>
</dl></dd>
<dt>aspf:</dt>
<dd><t>(plain-text; OPTIONAL; default is &quot;r&quot;.)  Indicates whether
strict or relaxed SPF Identifier Alignment mode is required by the
Domain Owner.  See <xref target="spf-identifiers"></xref> for details.  Valid values are as
follows:</t>

<dl>
<dt>r:</dt>
<dd>relaxed mode</dd>
<dt>s:</dt>
<dd>strict mode</dd>
</dl></dd>
<dt>fo:</dt>
<dd><t>Failure reporting options (plain-text; OPTIONAL; default is &quot;0&quot;)
Provides requested options for generation of failure reports.
Report generators MAY choose to adhere to the requested options.
This tag's content MUST be ignored if a &quot;ruf&quot; tag (below) is not
also specified.  Failure reporting options are shown below. The value
of this tag is either &quot;0&quot;, &quot;1&quot;, or a colon-separated list of the
options represented by alphabetic characters.</t>
</dd>
</dl>
<t>The valid values and their meanings are:</t>

<artwork>0:
:  Generate a DMARC failure report if all underlying
   authentication mechanisms fail to produce an aligned &quot;pass&quot;
   result.

1:
:  Generate a DMARC failure report if any underlying
   authentication mechanism produced something other than an
   aligned &quot;pass&quot; result.

d:
:  Generate a DKIM failure report if the message had a signature
   that failed evaluation, regardless of its alignment.  DKIM-
   specific reporting is described in [@!RFC6651].

s:
:  Generate an SPF failure report if the message failed SPF
   evaluation, regardless of its alignment.  SPF-specific
   reporting is described in [@!RFC6652].
</artwork>

<dl>
<dt>np:</dt>
<dd>Domain Owner Assessment Policy for non-existent subdomains
(plain-text; OPTIONAL).  Indicates the severity of concern the
Domain Owner or PSO has for mail using non-existent subdomains of the
domain queried. It applies only to non-existent subdomains of
the domain queried and not to either existing subdomains or
the domain itself.  Its syntax is identical to that of the &quot;p&quot;
tag defined below.  If the &quot;np&quot; tag is absent, the policy
specified by the &quot;sp&quot; tag (if the &quot;sp&quot; tag is present) or the
policy specified by the &quot;p&quot; tag, if the &quot;sp&quot; tag is not present,
MUST be applied for non-existent subdomains.  Note that &quot;np&quot; will
be ignored for DMARC records published on subdomains of Organizational
Domains and PSDs due to the effect of the DMARC policy discovery
mechanism described in <xref target="policy-discovery"></xref>.</dd>
<dt>p:</dt>
<dd><t>Domain Owner Assessment Policy (plain-text; RECOMMENDED for policy
records). Indicates the severity of concern the Domain Owner or PSO
has for mail using its domain but not passing DMARC verification.
Policy applies to the domain queried and to subdomains, unless
subdomain policy is explicitly described using the &quot;sp&quot; or &quot;np&quot; tags.
This tag is mandatory for policy records only, but not for third-party
reporting records (see <xref target="DMARC-Aggregate-Reporting"></xref> and <xref target="DMARC-Failure-Reporting"></xref>)
Possible values are as follows:</t>

<dl>
<dt>none:</dt>
<dd>The Domain Owner offers no expression of concern.</dd>
<dt>quarantine:</dt>
<dd>The Domain Owner considers such mail to be suspicious. It
is possible the mail is valid, although the failure creates
a significant concern.</dd>
<dt>reject:</dt>
<dd>The Domain Owner considers all such failures to be a clear
indication that the use of the domain name is not valid. See
<xref target="rejecting-messages"></xref> for some discussion of SMTP rejection
methods and their implications.</dd>
</dl></dd>
<dt>rua:</dt>
<dd><t>Addresses to which aggregate feedback is to be sent (comma-
separated plain-text list of DMARC URIs; OPTIONAL).  Section 3 of <xref target="DMARC-Aggregate-Reporting"></xref>
discusses considerations that apply when the domain name of a URI differs
from that of the domain advertising the policy.  See <xref target="external-report-addresses"></xref>
for additional considerations.  Any valid URI can be specified.<br />
A Mail Receiver MUST implement support for a &quot;mailto:&quot; URI, i.e., the
ability to send a DMARC report via electronic mail.  If not provided,
Mail Receivers MUST NOT generate aggregate feedback reports.  URIs
not supported by Mail Receivers MUST be ignored.  The aggregate
feedback report format is described in <xref target="DMARC-Aggregate-Reporting"></xref></t>
</dd>
<dt>ruf:</dt>
<dd><t>Addresses to which message-specific failure information is to
be reported (comma-separated plain-text list of DMARC URIs;
OPTIONAL).  If present, the Domain Owner or PSO is requesting Mail
Receivers to send detailed failure reports about messages that
fail the DMARC evaluation in specific ways (see the &quot;fo&quot; tag
above).  The format of the message to be generated MUST follow the
format specified for the &quot;rf&quot; tag. Section 3 of <xref target="DMARC-Aggregate-Reporting"></xref> discusses
considerations that apply when the domain name of a URI differs
from that of the domain advertising the policy.  A Mail Receiver
MUST implement support for a &quot;mailto:&quot; URI, i.e., the ability to
send a DMARC report via electronic mail.  If not provided, Mail
Receivers MUST NOT generate failure reports.  See <xref target="external-report-addresses"></xref> for
additional considerations.</t>
</dd>
<dt>sp:</dt>
<dd><t>Domain Owner Assessment Policy for all subdomains (plain-text;
OPTIONAL). Indicates the severity of concern the Domain Owner or PSO has
for mail using an existing subdomain of the domain queried but not
passing DMARC verification.  It applies only to subdomains of
the domain queried and not to the domain itself.  Its syntax is
identical to that of the &quot;p&quot; tag defined above.  If both the &quot;sp&quot;
tag is absent and the &quot;np&quot; tag is either absent or not applicable,
the policy specified by the &quot;p&quot; tag MUST be applied for subdomains.
Note that &quot;sp&quot; will be ignored for DMARC records published on
subdomains of Organizational Domains due to the effect of the
DMARC policy discovery mechanism described in <xref target="policy-discovery"></xref>.</t>
</dd>
<dt>t:</dt>
<dd><t>DMARC policy test mode (plain-text; OPTIONAL; default is 'n'). For
the RFC5322.From domain to which the DMARC record applies, the &quot;t&quot;
tag serves as a signal to the actor performing DMARC verification checks
as to whether or not the domain owner wishes the assessment policy
declared in the &quot;p=&quot;, &quot;sp=&quot;, and/or &quot;np=&quot; tags to actually be applied. This
parameter does not affect the generation of DMARC reports.  Possible values
are as follows:</t>

<dl>
<dt>y:</dt>
<dd>A request that the actor performing the DMARC verification check not
apply the policy, but instead apply any special handling rules it might have
in place, such as rewriting the RFC5322.From header.  The domain owner is
currently testing its specified DMARC assessment policy.</dd>
<dt>n:</dt>
<dd>The default, a request to apply the policy as specified to any
message that produces a DMARC &quot;fail&quot; result.</dd>
</dl></dd>
<dt>v:</dt>
<dd><t>Version (plain-text; REQUIRED).  Identifies the record retrieved
as a DMARC record.  It MUST have the value of &quot;DMARC1&quot;.  The value
of this tag MUST match precisely; if it does not or it is absent,
the entire retrieved record MUST be ignored.  It MUST be the first
tag in the list.</t>
</dd>
</dl>
<t>A DMARC policy record MUST comply with the formal specification found
in <xref target="formal-definition"></xref> in that the &quot;v&quot; tag MUST be present and MUST
appear first.  Unknown tags MUST be ignored.  Syntax errors
in the remainder of the record SHOULD be discarded in favor of
default values (if any) or ignored outright.</t>
<t>Note that given the rules of the previous paragraph, addition of a
new tag into the registered list of tags does not itself require a
new version of DMARC to be generated (with a corresponding change to
the &quot;v&quot; tag's value), but a change to any existing tags does require
a new version of DMARC.</t>
</section>

<section anchor="formal-definition"><name>Formal Definition</name>
<t>The formal definition of the DMARC format, using <xref target="RFC5234"></xref>, is as
follows:</t>

<artwork>  dmarc-uri       = URI 
                    ; &quot;URI&quot; is imported from [RFC3986]; commas (ASCII
                    ; 0x2C) and exclamation points (ASCII 0x21)
                    ; MUST be encoded

  dmarc-record    = dmarc-version dmarc-sep *(dmarc-tag dmarc-sep)

  dmarc-tag       = dmarc-request /
                    dmarc-test /
                    dmarc-srequest /
                    dmarc-nprequest /
                    dmarc-adkim /
                    dmarc-aspf /
                    dmarc-auri /
                    dmarc-furi /
                    dmarc-fo /
                    dmarc-rfmt 
                    ; components other than dmarc-version and
                    ; dmarc-request may appear in any order

  dmarc-version   = &quot;v&quot; *WSP &quot;=&quot; *WSP %x44 %x4d %x41 %x52 %x43 %x31

  dmarc-sep       = *WSP %x3b *WSP

  dmarc-request   = &quot;p&quot; *WSP &quot;=&quot; *WSP
                    ( &quot;none&quot; / &quot;quarantine&quot; / &quot;reject&quot; )

  dmarc-test      = &quot;t&quot; *WSP &quot;=&quot; ( &quot;y&quot; / &quot;n&quot; )

  dmarc-srequest  = &quot;sp&quot; *WSP &quot;=&quot; *WSP
                    ( &quot;none&quot; / &quot;quarantine&quot; / &quot;reject&quot; )

  dmarc-nprequest  = &quot;np&quot; *WSP &quot;=&quot; *WSP
                    ( &quot;none&quot; / &quot;quarantine&quot; / &quot;reject&quot; )

  dmarc-adkim     = &quot;adkim&quot; *WSP &quot;=&quot; *WSP ( &quot;r&quot; / &quot;s&quot; )

  dmarc-aspf      = &quot;aspf&quot; *WSP &quot;=&quot; *WSP ( &quot;r&quot; / &quot;s&quot; )

  dmarc-auri      = &quot;rua&quot; *WSP &quot;=&quot; *WSP
                    dmarc-uri *(*WSP &quot;,&quot; *WSP dmarc-uri)

  dmarc-furi      = &quot;ruf&quot; *WSP &quot;=&quot; *WSP
                    dmarc-uri *(*WSP &quot;,&quot; *WSP dmarc-uri)

  dmarc-fo        = &quot;fo&quot; *WSP &quot;=&quot; *WSP
                    ( &quot;0&quot; / &quot;1&quot; / ( &quot;d&quot; / &quot;s&quot; / &quot;d:s&quot; / &quot;s:d&quot; ) ) 

  dmarc-rfmt      = &quot;rf&quot;  *WSP &quot;=&quot; *WSP Keyword *(*WSP &quot;:&quot; Keyword)
                    ; registered reporting formats only

</artwork>
<t>&quot;Keyword&quot; is imported from Section 4.1.2 of <xref target="RFC5321"></xref>.</t>
</section>

<section anchor="domain-owner-actions"><name>Domain Owner Actions</name>
<t>This section describes Domain Owner actions to fully implement the
DMARC mechanism.</t>

<section anchor="publish-an-spf-policy-for-an-aligned-domain"><name>Publish an SPF Policy for an Aligned Domain</name>
<t>Because DMARC relies on SPF <xref target="RFC7208"></xref> and DKIM <xref target="RFC6376"></xref>, in
order to take full advantage of DMARC, a Domain Owner SHOULD first
ensure that SPF and DKIM authentication are properly configured.
The easiest first step here is to choose a domain to use as the
RFC5321.From domain (i.e., the Return-Path domain) for its mail,
one that aligns with the Author Domain, and then publish an SPF
policy in DNS for that domain.</t>
</section>

<section anchor="configure-sending-system-for-dkim-signing-using-an-aligned-domain"><name>Configure Sending System for DKIM Signing Using an Aligned Domain</name>
<t>While it is possible to secure a DMARC pass verdict based on only
SPF or DKIM, it is commonly accepted best practice to ensure that
both authentication mechanisms are in place in order to guard
against failure of just one of them. The Domain Owner SHOULD choose
a DKIM-Signing domain (i.e., the d= domain in the DKIM-Signature
header) that aligns with the Author Domain and configure its system
to sign using that domain.</t>
</section>

<section anchor="setup-a-mailbox-to-receive-aggregate-reports"><name>Setup a Mailbox to Receive Aggregate Reports</name>
<t>Proper consumption and analysis of DMARC aggregate reports is the
key to any successful DMARC deployment for a Domain Owner. DMARC
aggregate reports, which are XML documents and are defined in
<xref target="DMARC-Aggregate-Reporting"></xref>, contain valuable data for the Domain
Owner, showing sources of mail using the Author Domain. Depending
on how mature the Domain Owner's DMARC rollout is, some of these
sources could be legitimate ones that were overlooked during the
intial deployment of SPF and/or DKIM.</t>
<t>Because the aggregate reports are XML documents, it is strongly
advised that they be machine-parsed, so setting up a mailbox
involves more than just the physical creation of the mailbox. Many
third-party services exist that will process DMARC aggregate reports,
or the Domain Owner can create its own set of tools. No matter which
method is chosen, the ability to parse these reports and consume
the data contained in them will go a long way to ensuring a
successful deployment.</t>
</section>

<section anchor="publish-a-dmarc-policy-for-the-author-domain"><name>Publish a DMARC Policy for the Author Domain</name>
<t>Once SPF, DKIM, and the aggregate reports mailbox are all in place,
it's time to publish a DMARC record. For best results, Domain Owners
SHOULD start with &quot;p=none&quot;, with the rua tag containg the mailbox
created in the previous step.</t>
</section>

<section anchor="collect-and-analyze-reports-and-adjust-authentication"><name>Collect and Analyze Reports and Adjust Authentication</name>
<t>The reason for starting at &quot;p=none&quot; is to ensure that nothing's been
missed in the initial SPF and DKIM deployments. In all but the most
trivial setups, it is possible for a Domain Owner to overlook a
server here or be unaware of a third party sending agreeement there.
Starting at &quot;p=none&quot;, therefore, takes advantage of DMARC's aggregate
reporting function, with the Domain Owner using the reports to audit
its own mail streams. Should any overlooked systems be found in the
reports, the Domain Owner can adjust the SPF record and/or configure
DKIM signing for those systems.</t>
</section>

<section anchor="decide-if-and-when-to-update-dmarc-policy"><name>Decide If and When to Update DMARC Policy</name>
<t>Once the Domain Owner is satisfied that it is properly authenticating
all of its mail, then it is time to decide if it is appropriate to
change the p= value in its DMARC record to p=quarantine or p=reject.
Depending on its cadence for sending mail, it may take many months
of consuming DMARC aggregate reports before a Domain Owner reaches
the point where it is sure that it is properly authenticating all
of its mail, and the decision on which p= value to use will depend
on its needs.</t>
</section>
</section>

<section anchor="pso-actions"><name>PSO Actions</name>
<t>In addition to the DMARC Domain Owner actions, PSOs that require use
of DMARC and participate in PSD DMARC ought to make that information
availablle to Mail Receivers. <xref target="RFC9091"></xref> is an experimental
method for doing so, and the experiment is described in Appendix B
of that document.</t>
</section>

<section anchor="mail-receiver-actions"><name>Mail Receiver Actions</name>
<t>This section describes receiver actions in the DMARC environment.</t>

<section anchor="extract-author-domain"><name>Extract Author Domain</name>
<t>The domain in the RFC5322.From header field is extracted as the domain
to be evaluated by DMARC.  If the domain is encoded with UTF-8, the
domain name must be converted to an A-label, as described in Section
2.3 of <xref target="RFC5890"></xref>, for further processing.</t>
<t>In order to be processed by DMARC, a message typically needs to
contain exactly one RFC5322.From domain (a single From: field with a
single domain in it). Not all messages meet this requirement, and
the handling of those that are forbidden under <xref target="RFC5322"></xref> or that
contain no meaningful domains is outside the scope of this document.</t>
<t>The case of a syntactically valid multi-valued RFC5322.From header
field presents a particular challenge. When a single RFC5322.From
header field contains multiple addresses, it is possible that there
may be multiple domains used in those addresses. The process in this
case is to only proceed with DMARC checking if the domain is
identical for all of the addresses in a multi-valued RFC5322.From
header field. Multi-valued RFC5322.From header fields with multiple
domains MUST be exempt from DMARC checking.</t>
<t>Note that domain names that appear on a public suffix list are not
exempt from DMARC policy application and reporting.</t>
</section>

<section anchor="determine-handling-policy"><name>Determine Handling Policy</name>
<t>To arrive at a policy for an individual message, Mail Receivers MUST
perform the following actions or their semantic equivalents.
Steps 2-4 MAY be done in parallel, whereas steps 5 and 6 require
input from previous steps.</t>
<t>The steps are as follows:</t>

<ol>
<li><t>Extract the RFC5322.From domain from the message (as above).</t>
</li>
<li><t>Query the DNS for a DMARC policy record.  Continue if one is
found, or terminate DMARC evaluation otherwise.  See
<xref target="policy-discovery"></xref> for details.</t>
</li>
<li><t>Perform DKIM signature verification checks.  A single email could
contain multiple DKIM signatures.  The results of this step are
passed to the remainder of the algorithm, MUST include &quot;pass&quot; or
&quot;fail&quot;, and if &quot;fail&quot;, SHOULD include information about the reasons
for failure. The results MUST further include the value of the &quot;d=&quot;
and &quot;s=&quot; tags from each checked DKIM signature.</t>
</li>
<li><t>Perform SPF verification checks.  The results of this step are
passed to the remainder of the algorithm, MUST include &quot;pass&quot; or
&quot;fail&quot;, and if &quot;fail&quot;, SHOULD include information about the reasons
for failure. The results MUST further include the domain name used
to complete the SPF check.</t>
</li>
<li><t>Conduct Identifier Alignment checks.  With authentication checks
and policy discovery performed, the Mail Receiver checks to see
if Authenticated Identifiers fall into alignment as described in
<xref target="terminology"></xref>.  If one or more of the Authenticated Identifiers align
with the RFC5322.From domain, the message is considered to pass
the DMARC mechanism check.  All other conditions (authentication
failures, identifier mismatches) are considered to be DMARC
mechanism check failures.</t>
</li>
<li><t>Apply policy.  Emails that fail the DMARC mechanism check are
handled in accordance with the discovered DMARC policy of the
Domain Owner and any local policy rules enforced by the Mail Receiver.
See <xref target="general-record-format"></xref> for details.</t>
</li>
</ol>
<t>Heuristics applied in the absence of use by a Domain Owner of either
SPF or DKIM (e.g., <xref target="Best-Guess-SPF"></xref>) SHOULD NOT be used, as it may be
the case that the Domain Owner wishes a Message Receiver not to
consider the results of that underlying authentication protocol at
all.</t>
<t>DMARC evaluation can only yield a &quot;pass&quot; result after one of the
underlying authentication mechanisms passes for an aligned
identifier.  If neither passes and one or both of them fail due to a
temporary error, the Receiver evaluating the message is unable to
conclude that the DMARC mechanism had a permanent failure; they
therefore cannot apply the advertised DMARC policy.  When otherwise
appropriate, Receivers MAY send feedback reports regarding temporary
errors.</t>
<t>Handling of messages for which SPF and/or DKIM evaluation encounter a
permanent DNS error is left to the discretion of the Mail Receiver.</t>
</section>

<section anchor="policy-discovery"><name>Policy Discovery</name>
<t>As stated above, the DMARC mechanism uses DNS TXT records to
advertise policy.  Policy discovery is accomplished via a method
similar to the method used for SPF records.  This method, and the
important differences between DMARC and SPF mechanisms, are discussed
below.</t>
<t>To balance the conflicting requirements of supporting wildcarding,
allowing subdomain policy overrides, and limiting DNS query load, the
following DNS lookup scheme is employed:</t>

<ol>
<li><t>Mail Receivers MUST query the DNS for a DMARC TXT record at the
DNS domain matching the one found in the RFC5322.From domain in
the message.  A possibly empty set of records is returned.</t>
</li>
<li><t>Records that do not start with a &quot;v=&quot; tag that identifies the
current version of DMARC are discarded.</t>
</li>
<li><t>If the set is now empty, the Mail Receiver MUST query the DNS for
a DMARC TXT record at the DNS domain matching the Organizational
Domain in place of the RFC5322.From domain in the message (if
different).  This record can contain policy to be asserted for
subdomains of the Organizational Domain.  A possibly empty set of
records is returned.</t>
</li>
<li><t>Records that do not start with a &quot;v=&quot; tag that identifies the
current version of DMARC are discarded.</t>
</li>
<li><t>If the set is now empty and the longest PSD <xref target="longest-psd"></xref> of the
Organizational Domain is one that the receiver has determined is
acceptable for PSD DMARC (based on the data in one of the DMARC
PSD Registry Examples decribed in Appendix B of <xref target="RFC9091"></xref>)
the Mail Receiver MUST query the DNS for a DMARC TXT record at
the DNS domain matching the longest PSD in place of the RFC5322.From
domain in the message (if different).  A possibly empty set of records
is returned.</t>
</li>
<li><t>Records that do not start with a &quot;v=&quot; tag that identifies the
current version of DMARC are discarded.</t>
</li>
<li><t>If the remaining set contains multiple records or no records,
policy discovery terminates and DMARC processing is not applied
to this message.</t>
</li>
<li><t>If a retrieved policy record does not contain a valid &quot;p&quot; tag, or
contains an &quot;sp&quot; tag that is not valid, then:</t>

<ol>
<li><t>if a &quot;rua&quot; tag is present and contains at least one
syntactically valid reporting URI, the Mail Receiver SHOULD
act as if a record containing a valid &quot;v&quot; tag and &quot;p=none&quot;
was retrieved, and continue processing;</t>
</li>
<li><t>otherwise, the Mail Receiver applies no DMARC processing to
this message.</t>
</li>
</ol></li>
</ol>
<t>If the set produced by the mechanism above contains no DMARC policy
record (i.e., any indication that there is no such record as opposed
to a transient DNS error), Mail Receivers SHOULD NOT apply the DMARC
mechanism to the message.</t>
<t>Handling of DNS errors when querying for the DMARC policy record is
left to the discretion of the Mail Receiver.  For example, to ensure
minimal disruption of mail flow, transient errors could result in
delivery of the message (&quot;fail open&quot;), or they could result in the
message being temporarily rejected (i.e., an SMTP 4yx reply), which
invites the sending MTA to try again after the condition has possibly
cleared, allowing a definite DMARC conclusion to be reached (&quot;fail
closed&quot;).</t>

<section anchor="longest-psd-example"><name>Longest PSD Example</name>
<t>As an example of step 5 above, for a message with the Organizational
Domain of &quot;example.compute.cloudcompany.com.example&quot;, the query for
PSD DMARC would use &quot;compute.cloudcompany.com.example&quot; as the longest
PSD. The receiver would check to see if that PSD is listed in the DMARC
PSD Registry, and if so, perform the policy lookup at
&quot;_dmarc.compute.cloudcompany.com.example&quot;.</t>
<t>Note: Because the PSD policy query comes after the Organizational
Domain policy query, PSD policy is not used for Organizational
domains that have published a DMARC policy.  Specifically, this is
not a mechanism to provide feedback addresses (RUA/RUF) when an
Organizational Domain has declined to do so.</t>
</section>
</section>

<section anchor="store-results-of-dmarc-processing"><name>Store Results of DMARC Processing</name>
<t>The results of Mail Receiver-based DMARC processing should be stored
for eventual presentation back to the Domain Owner in the form of
aggregate feedback reports.  <xref target="general-record-format"></xref> and
<xref target="DMARC-Aggregate-Reporting"></xref> discuss aggregate feedback.</t>
</section>

<section anchor="send-aggregate-reports"><name>Send Aggregate Reports</name>
<t>For a Domain Owner, DMARC aggregate reports provide data about all
mailstreams making use of its domain in email, to include not only
illegitimate uses but also, and perhaps more importantly, all
legitimate uses. Domain Owners can use aggregate reports to ensure
that all legitimate uses of their domain for sending email are
properly authenticated, and once they are, increase the severity of
concern expressed in the p= tag in their DMARC policy records from
none to quarantine to reject, if appropriate. In turn, DMARC policy
records with p= tag values of 'quarantine' or 'reject' are higher
value signals to Mail Receivers, ones that can assist Mail Receivers
with handling decisions for a message in ways that p= tag values of
'none' cannot.</t>
<t>In order to ensure maximum usefulness for DMARC across the email
ecosystem, then, Mail Receivers MUST generate and send aggregate
reports with a frequency of at least once every 24 hours.</t>
</section>
</section>

<section anchor="policy-enforcement-considerations"><name>Policy Enforcement Considerations</name>
<t>Mail Receivers MAY choose to reject or quarantine email even if email
passes the DMARC mechanism check. The DMARC mechanism does not
inform Mail Receivers whether an email stream is &quot;good&quot;; a DMARC result
of &quot;pass&quot; only means that the domain in the RFC5322.From header has been
verified by the DMARC mechanism. Mail Receivers are encouraged to maintain
anti-abuse technologies to combat the possibility of DMARC-enabled criminal
campaigns.</t>
<t>Mail Receivers MAY choose to accept email that fails the DMARC
mechanism check even if the published Domain Owner Assessment Policy
is &quot;reject&quot;.  Mail Receivers need to make a best effort not to increase
the likelihood of accepting abusive mail if they choose not to honor
the published Domain Owner Assessment Policy.  At a minimum, addition
of the Authentication-Results header field (see <xref target="RFC8601"></xref>) is
RECOMMENDED when delivery of failing mail is done.  When this is
done, the DNS domain name thus recorded MUST be encoded as an
A-label.</t>
<t>Mail Receivers are only obligated to report reject or quarantine
policy actions in aggregate feedback reports that are due to published
DMARC Domain Owner Assessment Policy. They are not required to report
reject or quarantine actions that are the result of local policy. If
local policy information is exposed, abusers can gain insight into the
effectiveness and delivery rates of spam campaigns.</t>
<t>Final handling of a message is always a matter of local policy.
An operator that wishes to favor DMARC policy over SPF policy, for
example, will disregard the SPF policy, since enacting an
SPF-determined rejection prevents evaluation of DKIM; DKIM might
otherwise pass, satisfying the DMARC evaluation.  There is a
trade-off to doing so, namely acceptance and processing of the entire
message body in exchange for the enhanced protection DMARC provides.</t>
<t>DMARC-compliant Mail Receivers typically disregard any mail-handling
directive discovered as part of an authentication mechanism (e.g.,
Author Domain Signing Practices (ADSP), SPF) where a DMARC record is
also discovered that specifies a policy other than &quot;none&quot;.  Deviating
from this practice introduces inconsistency among DMARC operators in
terms of handling of the message.  However, such deviation is not
proscribed.</t>
<t>To enable Domain Owners to receive DMARC feedback without impacting
existing mail processing, discovered policies of &quot;p=none&quot; SHOULD NOT
modify existing mail handling processes.</t>
<t>Mail Receivers MUST also implement reporting instructions of DMARC,
even in the absence of a request for DKIM reporting <xref target="RFC6651"></xref> or
SPF reporting <xref target="RFC6652"></xref>.  Furthermore, the presence of such requests
SHOULD NOT affect DMARC reporting.</t>
</section>
</section>

<section anchor="dmarc-feedback"><name>DMARC Feedback</name>
<t>Providing Domain Owners with visibility into how Mail Receivers
implement and enforce the DMARC mechanism in the form of feedback is
critical to establishing and maintaining accurate authentication
deployments.  When Domain Owners can see what effect their policies
and practices are having, they are better willing and able to use
quarantine and reject policies.</t>
<t>The details of this feedback are described in <xref target="DMARC-Aggregate-Reporting"></xref></t>
<t>Operational note for PSD DMARC: For PSOs, feedback for non-existent
domains is desirable and useful, just as it is for org-level DMARC
operators.  See Section 4 of <xref target="RFC9091"></xref> for discussion of
Privacy Considerations for PSD DMARC</t>
</section>

<section anchor="minimum-implementations"><name>Minimum Implementations</name>
<t>Domain owners, mediators, and mail receivers can all claim to
implement DMARC, but what that means will depend on their role in the
transmission of mail. To remove any ambiguity from the claims, this
document specifies the following minimum criteria that must be met
for each agent to rightly claim to be &quot;implementing DMARC&quot;.</t>
<t>Domain Owner: To implement DMARC, a Domain Owner MUST configure its
domain to convey its concern that unauthenticated mail be rejected
or at least treated with suspicion. Furthermore, the Domain Owner MUST
actively solicit aggregate feedback reports regarding mail using its
domain. This means that it MUST publish a policy record that:</t>

<ul>
<li>Has a p tag with a value of 'quarantine' or 'reject'</li>
<li>Has a rua tag with at least one valid URI</li>
<li>If applicable, has an sp tag with a value of 'quarantine' or
'reject'</li>
<li>If desired, has an np tag with a value of 'quarantine' or
'reject'</li>
</ul>
<t>While 'none' is a syntactically valid value for both p, sp, and np
tags, the practical value of any of those tags being 'none' means
that the Domain Owner is still gathering information about mail
flows for the domain or sub-domains. It is not yet ready to commit
to conveying a severity of concern for unauthenticated email using
its domain.</t>
<t>Mediator: To implement DMARC, a mediator MUST do the following before
passing the message to the next hop or rejecting it as appropriate:</t>

<ul>
<li>Perform DMARC verification checks on inbound mail</li>
<li>Perform verification on any authentication checks recorded by
previous mediators.</li>
<li>Record the results of its authentication checks in message
headers for consumption by later hosts.</li>
</ul>
<t>Mail Receiver: To implement DMARC, a mail receiver MUST do the
following:</t>

<ul>
<li>Perform DMARC verification checks on inbound mail</li>
<li>Perform verification checks on any authentication check results
recorded by mediators that handled the message prior to its
reaching the Mail Receiver.</li>
<li>Send aggregate reports to Domain Owners at least every 24 hours
when a minimum of 100 messages with that domain in the RFC5322.From
header field have been seen during the reporting period</li>
</ul>
</section>

<section anchor="other-topics"><name>Other Topics</name>
<t>This section discusses some topics regarding choices made in the
development of DMARC, largely to commit the history to record.</t>

<section anchor="issues-specific-to-spf"><name>Issues Specific to SPF</name>
<t>Though DMARC does not inherently change the semantics of an SPF
policy record, historically lax enforcement of such policies has led
many to publish extremely broad records containing many large network
ranges.  Domain Owners are strongly encouraged to carefully review
their SPF records to understand which networks are authorized to send
on behalf of the Domain Owner before publishing a DMARC record.</t>
<t>Some receiver architectures might implement SPF in advance of any
DMARC operations.  This means that a &quot;-&quot; prefix on a sender's SPF
mechanism, such as &quot;-all&quot;, could cause that rejection to go into
effect early in handling, causing message rejection before any DMARC
processing takes place.  Operators choosing to use &quot;-all&quot; should be
aware of this.</t>
</section>

<section anchor="dns-load-and-caching"><name>DNS Load and Caching</name>
<t>DMARC policies are communicated using the DNS and therefore inherit a
number of considerations related to DNS caching.  The inherent
conflict between freshness and the impact of caching on the reduction
of DNS-lookup overhead should be considered from the Mail Receiver's
point of view.  Should Domain Owners or PSOs publish a DNS record with a very
short TTL, Mail Receivers can be provoked through the injection of
large volumes of messages to overwhelm the publisher's DNS.
Although this is not a concern specific to DMARC, the implications of
a very short TTL should be considered when publishing DMARC policies.</t>
<t>Conversely, long TTLs will cause records to be cached for long
periods of time.  This can cause a critical change to DMARC
parameters advertised by a Domain Owner or PSO to go unnoticed for the
length of the TTL (while waiting for DNS caches to expire).  Avoiding
this problem can mean shorter TTLs, with the potential problems
described above.  A balance should be sought to maintain
responsiveness of DMARC preference changes while preserving the
benefits of DNS caching.</t>
</section>

<section anchor="rejecting-messages"><name>Rejecting Messages</name>
<t>This protocol calls for rejection of a message during the SMTP
session under certain circumstances.  This is preferable to
generation of a Delivery Status Notification (<xref target="RFC3464"></xref>), since
fraudulent messages caught and rejected using DMARC would then result
in annoying generation of such failure reports that go back to the
RFC5321.MailFrom address.</t>
<t>This synchronous rejection is typically done in one of two ways:</t>

<ul>
<li><t>Full rejection, wherein the SMTP server issues a 5xy reply code as
an indication to the SMTP client that the transaction failed; the
SMTP client is then responsible for generating notification that
delivery failed (see Section 4.2.5 of <xref target="RFC5321"></xref>).</t>
</li>
<li><t>A &quot;silent discard&quot;, wherein the SMTP server returns a 2xy reply
code implying to the client that delivery (or, at least, relay)
was successfully completed, but then simply discarding the message
with no further action.</t>
</li>
</ul>
<t>Each of these has a cost.  For instance, a silent discard can help to
prevent backscatter, but it also effectively means that the SMTP
server has to be programmed to give a false result, which can
confound external debugging efforts.</t>
<t>Similarly, the text portion of the SMTP reply may be important to
consider.  For example, when rejecting a message, revealing the
reason for the rejection might give an attacker enough information to
bypass those efforts on a later attempt, though it might also assist
a legitimate client to determine the source of some local issue that
caused the rejection.</t>
<t>In the latter case, when doing an SMTP rejection, providing a clear
hint can be useful in resolving issues.  A receiver might indicate in
plain text the reason for the rejection by using the word &quot;DMARC&quot;
somewhere in the reply text.  Many systems are able to scan the SMTP
reply text to determine the nature of the rejection.  Thus, providing
a machine-detectable reason for rejection allows the problems causing
rejections to be properly addressed by automated systems.  For
example:</t>

<artwork>550 5.7.1 Email rejected per DMARC policy for example.com
</artwork>
<t>If a Mail Receiver elects to defer delivery due to inability to
retrieve or apply DMARC policy, this is best done with a 4xy SMTP
reply code.</t>
</section>

<section anchor="identifier-alignment-considerations"><name>Identifier Alignment Considerations</name>
<t>The DMARC mechanism allows both DKIM and SPF-authenticated
identifiers to authenticate email on behalf of a Domain Owner and,
possibly, on behalf of different subdomains.  If malicious or unaware
users can gain control of the SPF record or DKIM selector records for
a subdomain, the subdomain can be used to generate DMARC-passing
email on behalf of the Organizational Domain.</t>
<t>For example, an attacker who controls the SPF record for
&quot;evil.example.com&quot; can send mail with an RFC5322.From header field
containing &quot;foo@example.com&quot; that can pass both authentication and
the DMARC check against &quot;example.com&quot;.</t>
<t>The Organizational Domain administrator should be careful not to
delegate control of subdomains if this is an issue, and to consider
using the &quot;strict&quot; Identifier Alignment option if appropriate.</t>
</section>

<section anchor="interoperability-issues"><name>Interoperability Issues</name>
<t>DMARC limits which end-to-end scenarios can achieve a &quot;pass&quot; result.</t>
<t>Because DMARC relies on SPF <xref target="RFC7208"></xref> and/or DKIM <xref target="RFC6376"></xref> to achieve
a &quot;pass&quot;, their limitations also apply.</t>
<t>Additional DMARC constraints occur when a message is processed by
some Mediators, such as mailing lists.  Transiting a Mediator often
causes either the authentication to fail or Identifier Alignment to
be lost.  These transformations may conform to standards but will
still prevent a DMARC &quot;pass&quot;.</t>
<t>In addition to Mediators, mail that is sent by authorized,
independent third parties might not be sent with Identifier
Alignment, also preventing a &quot;pass&quot; result.</t>
<t>Issues specific to the use of policy mechanisms alongside DKIM are
further discussed in <xref target="RFC6377"></xref>, particularly Section 5.2.</t>
</section>
</section>

<section anchor="iana-considerations"><name>IANA Considerations</name>
<t>This section describes actions completed by IANA.</t>

<section anchor="authentication-results-method-registry-update"><name>Authentication-Results Method Registry Update</name>
<t>IANA has added the following to the &quot;Email Authentication Methods&quot;
registry:</t>
<table align="left"><name>&quot;Authentication-Results Method Registry Update&quot;
</name>
<thead>
<tr>
<th align="left">Method</th>
<th align="left">Defined</th>
<th align="left">ptype</th>
<th align="left">Property</th>
<th align="left">Value</th>
<th align="left">Status</th>
<th align="left">Version</th>
</tr>
</thead>

<tbody>
<tr>
<td align="left">dmarc</td>
<td align="left"><xref target="RFC7489"></xref></td>
<td align="left">header</td>
<td align="left">from</td>
<td align="left">the domain portion of the RFC5322.From header field</td>
<td align="left">active</td>
<td align="left">1</td>
</tr>

<tr>
<td align="left">dmarc</td>
<td align="left"><xref target="RFC7489"></xref></td>
<td align="left">polrec</td>
<td align="left">p</td>
<td align="left">the p= value read from the discovered policy record</td>
<td align="left">active</td>
<td align="left">1</td>
</tr>

<tr>
<td align="left">dmarc</td>
<td align="left"><xref target="RFC7489"></xref></td>
<td align="left">polrec</td>
<td align="left">domain</td>
<td align="left">the domain at which the policy record was discovered, if different from the RFC5322.From domain</td>
<td align="left">active</td>
<td align="left">1</td>
</tr>
</tbody>
</table></section>

<section anchor="authentication-results-result-registry-update"><name>Authentication-Results Result Registry Update</name>
<t>IANA has added the following in the &quot;Email Authentication Result
Names&quot; registry:</t>
<table align="left"><name>&quot;Authentication-Results Result Registry Update&quot;
</name>
<thead>
<tr>
<th align="left">Code</th>
<th align="left">Existing/New Code</th>
<th align="left">Defined</th>
<th align="left">Auth Method</th>
<th align="left">Meaning</th>
<th align="left">Status</th>
</tr>
</thead>

<tbody>
<tr>
<td align="left">none</td>
<td align="left">existing</td>
<td align="left"><xref target="RFC8601"></xref></td>
<td align="left">dmarc (added)</td>
<td align="left">No DMARC policy record was published for the aligned identifier, or no aligned identifier could be extracted.</td>
<td align="left">active</td>
</tr>

<tr>
<td align="left">pass</td>
<td align="left">existing</td>
<td align="left"><xref target="RFC8601"></xref></td>
<td align="left">dmarc (added)</td>
<td align="left">A DMARC policy record was published for the aligned identifier, and at least one of the authentication mechanisms passed.</td>
<td align="left">active</td>
</tr>

<tr>
<td align="left">fail</td>
<td align="left">existing</td>
<td align="left"><xref target="RFC8601"></xref></td>
<td align="left">dmarc (added)</td>
<td align="left">A DMARC policy record was published for the aligned identifier, and none of the authentication mechanisms passed.</td>
<td align="left">active</td>
</tr>

<tr>
<td align="left">temperror</td>
<td align="left">existing</td>
<td align="left"><xref target="RFC8601"></xref></td>
<td align="left">dmarc (added)</td>
<td align="left">A temporary error occurred during DMARC evaluation. A later attempt might produce a final result.</td>
<td align="left">active</td>
</tr>

<tr>
<td align="left">permerror</td>
<td align="left">existing</td>
<td align="left"><xref target="RFC8601"></xref></td>
<td align="left">dmarc (added)</td>
<td align="left">A permanent error occurred during DMARC evaluation, such as encountering a syntactically incorrect DMARC record. A later attempt is unlikely to produce a final result.</td>
<td align="left">active</td>
</tr>
</tbody>
</table></section>

<section anchor="feedback-report-header-fields-registry-update"><name>Feedback Report Header Fields Registry Update</name>
<t>The following has been added to the &quot;Feedback Report Header Fields&quot;
registry:</t>
<t>Field Name:  Identity-Alignment</t>

<dl>
<dt>Description:</dt>
<dd>indicates whether the message about which a report is
being generated had any identifiers in alignment as defined in
RFC 7489</dd>
</dl>
<t>Multiple Appearances:  No</t>
<t>Related &quot;Feedback-Type&quot;:  auth-failure</t>
<t>Reference:  RFC 7489</t>
<t>Status:  current</t>
</section>

<section anchor="dmarc-tag-registry"><name>DMARC Tag Registry</name>
<t>A new registry tree called &quot;Domain-based Message Authentication,
Reporting, and Conformance (DMARC) Parameters&quot; has been created.
Within it, a new sub-registry called the &quot;DMARC Tag Registry&quot; has
been created.</t>
<t>Names of DMARC tags must be registered with IANA in this new
sub-registry.  New entries are assigned only for values that have
been documented in a manner that satisfies the terms of Specification
Required, per <xref target="RFC8126"></xref>.  Each registration must include
the tag name; the specification that defines it; a brief description;
and its status, which must be one of &quot;current&quot;, &quot;experimental&quot;, or
&quot;historic&quot;.  The Designated Expert needs to confirm that the provided
specification adequately describes the new tag and clearly presents
how it would be used within the DMARC context by Domain Owners and
Mail Receivers.</t>
<t>To avoid version compatibility issues, tags added to the DMARC
specification are to avoid changing the semantics of existing records
when processed by implementations conforming to prior specifications.</t>
<t>The initial set of entries in this registry is as follows:</t>
<table align="left"><name>&quot;DMARC Tag Registry&quot;
</name>
<thead>
<tr>
<th align="left">Tag Name</th>
<th align="left">Reference</th>
<th align="left">Status</th>
<th align="left">Description</th>
</tr>
</thead>

<tbody>
<tr>
<td align="left">adkim</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">DKIM alignment mode</td>
</tr>

<tr>
<td align="left">aspf</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">SPF alignment mode</td>
</tr>

<tr>
<td align="left">fo</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Failure reporting options</td>
</tr>

<tr>
<td align="left">p</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Requested handling policy</td>
</tr>

<tr>
<td align="left">pct</td>
<td align="left">RFC 7489</td>
<td align="left">historic</td>
<td align="left">Sampling rate</td>
</tr>

<tr>
<td align="left">rf</td>
<td align="left">RFC 7489</td>
<td align="left">historic</td>
<td align="left">Failure reporting format(s)</td>
</tr>

<tr>
<td align="left">ri</td>
<td align="left">RFC 7489</td>
<td align="left">historic</td>
<td align="left">Aggregate Reporting interval</td>
</tr>

<tr>
<td align="left">rua</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Reporting URI(s) for aggregate data</td>
</tr>

<tr>
<td align="left">ruf</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Reporting URI(s) for failure data</td>
</tr>

<tr>
<td align="left">sp</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Requested handling policy for subdomains</td>
</tr>

<tr>
<td align="left">t</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Test mode for the specified policy</td>
</tr>

<tr>
<td align="left">v</td>
<td align="left">RFC 7489</td>
<td align="left">current</td>
<td align="left">Specification version</td>
</tr>
</tbody>
</table></section>

<section anchor="dmarc-report-format-registry"><name>DMARC Report Format Registry</name>
<t>Also within &quot;Domain-based Message Authentication, Reporting, and
Conformance (DMARC) Parameters&quot;, a new sub-registry called &quot;DMARC
Report Format Registry&quot; has been created.</t>
<t>Names of DMARC failure reporting formats must be registered with IANA
in this registry.  New entries are assigned only for values that
satisfy the definition of Specification Required, per
<xref target="RFC8126"></xref>.  In addition to a reference to a permanent
specification, each registration must include the format name; a
brief description; and its status, which must be one of &quot;current&quot;,
&quot;experimental&quot;, or &quot;historic&quot;.  The Designated Expert needs to
confirm that the provided specification adequately describes the
report format and clearly presents how it would be used within the
DMARC context by Domain Owners and Mail Receivers.</t>
<t>The initial entry in this registry is as follows:</t>
<table align="left"><name>&quot;DMARC Report Format Registry&quot;
</name>
<thead>
<tr>
<th>Format Name</th>
<th>Reference</th>
<th>Status</th>
<th>Description</th>
</tr>
</thead>

<tbody>
<tr>
<td>afrf</td>
<td>RFC 7489</td>
<td>current</td>
<td>Authentication Failure Reporting Format (see <xref target="RFC6591"></xref>)</td>
</tr>
</tbody>
</table></section>

<section anchor="underscored-and-globally-scoped-dns-node-names-registry"><name>Underscored and Globally Scoped DNS Node Names Registry</name>
<t>Per <xref target="RFC8552"></xref>, please add the following entry to the &quot;Underscored
and Globally Scoped DNS Node Names&quot; registry:</t>
<table align="left"><name>&quot;Underscored and Globally Scoped DNS Node Names&quot; registry
</name>
<thead>
<tr>
<th>RR Type</th>
<th>_NODE NAME</th>
<th>Reference</th>
</tr>
</thead>

<tbody>
<tr>
<td>TXT</td>
<td>_dmarc</td>
<td>RFC 7489</td>
</tr>
</tbody>
</table></section>
</section>

<section anchor="security-considerations"><name>Security Considerations</name>
<t>This section discusses security issues and possible remediations
(where available) for DMARC.</t>

<section anchor="authentication-methods"><name>Authentication Methods</name>
<t>Security considerations from the authentication methods used by DMARC
are incorporated here by reference.</t>
</section>

<section anchor="attacks-on-reporting-uris"><name>Attacks on Reporting URIs</name>
<t>URIs published in DNS TXT records are well-understood possible
targets for attack.  Specifications such as <xref target="RFC1035"></xref> and <xref target="RFC2142"></xref> either
expose or cause the exposure of email addresses that could be flooded
by an attacker, for example; MX, NS, and other records found in the
DNS advertise potential attack destinations; common DNS names such as
&quot;www&quot; plainly identify the locations at which particular services can
be found, providing destinations for targeted denial-of-service or
penetration attacks.</t>
<t>Thus, Domain Owners will need to harden these addresses against
various attacks, including but not limited to:</t>

<ul>
<li><t>high-volume denial-of-service attacks;</t>
</li>
<li><t>deliberate construction of malformed reports intended to identify
or exploit parsing or processing vulnerabilities;</t>
</li>
<li><t>deliberate construction of reports containing false claims for the
Submitter or Reported-Domain fields, including the possibility of
false data from compromised but known Mail Receivers.</t>
</li>
</ul>
</section>

<section anchor="dns-security"><name>DNS Security</name>
<t>The DMARC mechanism and its underlying technologies (SPF, DKIM)
depend on the security of the DNS. Examples of how hostile parties can
have an adverse impact on DNS traffic include:
*  If they can snoop on DNS traffic, they can get an idea of who is
   sending mail.</t>

<ul>
<li><t>If they can block outgoing or reply DNS messages, they can prevent
systems from discovering senders' DMARC policies, causing recipients
to assume p=none by default.</t>
</li>
<li><t>If they can send forged response packets, they can make aligned mail
appear unaligned or vice-versa.</t>
</li>
</ul>
<t>None of these threats are unique to DMARC, and they can be addressed using
a variety of techniques, including, but not limited to:</t>

<ul>
<li><t>Signing DNS records with DNSSEC <xref target="RFC4033"></xref>, which enables recipients to
detect and discard forged responses.</t>
</li>
<li><t>DNS over TLS <xref target="RFC7858"></xref> or DNS over HTTPS <xref target="RFC8484"></xref> can mitigate snooping
and forged responses.</t>
</li>
</ul>
</section>

<section anchor="display-name-attacks"><name>Display Name Attacks</name>
<t>A common attack in messaging abuse is the presentation of false
information in the display-name portion of the RFC5322.From header field.
For example, it is possible for the email address in that field to be
an arbitrary address or domain name, while containing a well-known
name (a person, brand, role, etc.) in the display name, intending to
fool the end user into believing that the name is used legitimately.
The attack is predicated on the notion that most common MUAs will
show the display name and not the email address when both are
available.</t>
<t>Generally, display name attacks are out of scope for DMARC, as
further exploration of possible defenses against these attacks needs
to be undertaken.</t>
<t>There are a few possible mechanisms that attempt mitigation of these
attacks, such as the following:</t>

<ul>
<li><t>If the display name is found to include an email address (as
specified in <xref target="RFC5322"></xref>), execute the DMARC mechanism on the domain
name found there rather than the domain name discovered
originally.  However, this addresses only a very specific attack
space, and spoofers can easily circumvent it by simply not using
an email address in the display name.  There are also known cases
of legitimate uses of an email address in the display name with a
domain different from the one in the address portion, e.g.,</t>
<t>From: &quot;user@example.org via Bug Tracker&quot; <eref target="mailto:support@example.com">support@example.com</eref></t>
</li>
<li><t>In the MUA, only show the display name if the DMARC mechanism
succeeds.  This too is easily defeated, as an attacker could
arrange to pass the DMARC tests while fraudulently using another
domain name in the display name.</t>
</li>
<li><t>In the MUA, only show the display name if the DMARC mechanism
passes and the email address thus verified matches one found in
the receiving user's list of known addresses.</t>
</li>
</ul>
</section>

<section anchor="external-report-addresses"><name>External Reporting Addresses</name>
<t>To avoid abuse by bad actors, reporting addresses generally have to
be inside the domains about which reports are requested.  In order to
accommodate special cases such as a need to get reports about domains
that cannot actually receive mail, Section 3 of <xref target="DMARC-Aggregate-Reporting"></xref> describes
a DNS-based mechanism for verifying approved external reporting.</t>
<t>The obvious consideration here is an increased DNS load against
domains that are claimed as external recipients.  Negative caching
will mitigate this problem, but only to a limited extent, mostly
dependent on the default TTL in the domain's SOA record.</t>
<t>Where possible, external reporting is best achieved by having the
report be directed to domains that can receive mail and simply having
it automatically forwarded to the desired external destination.</t>
<t>Note that the addresses shown in the &quot;ruf&quot; tag receive more
information that might be considered private data, since it is
possible for actual email content to appear in the failure reports.
The URIs identified there are thus more attractive targets for
intrusion attempts than those found in the &quot;rua&quot; tag.  Moreover,
attacking the DNS of the subject domain to cause failure data to be
routed fraudulently to an attacker's systems may be an attractive
prospect.  Deployment of <xref target="RFC4033"></xref> is advisable if this is a concern.</t>
</section>

<section anchor="secure-protocols"><name>Secure Protocols</name>
<t>This document encourages use of secure transport mechanisms to
prevent loss of private data to third parties that may be able to
monitor such transmissions.  Unencrypted mechanisms should be
avoided.</t>
<t>In particular, a message that was originally encrypted or otherwise
secured might appear in a report that is not sent securely, which
could reveal private information.</t>
</section>
</section>

</middle>

<back>
<references><name>Normative References</name>
<reference anchor="DMARC-Aggregate-Reporting" target="https://datatracker.ietf.org/doc/draft-ietf-dmarc-aggregate-reporting/">
  <front>
    <title>DMARC Aggregate Reporting</title>
    <author fullname="Alex Brotman" initials="A." surname="Brotman" role="editor">
      <organization>Comcast, Inc.</organization>
    </author>
    <date year="2021" month="February"></date>
  </front>
</reference>
<reference anchor="DMARC-Failure-Reporting" target="https://datatracker.ietf.org/doc/draft-ietf-dmarc-failure-reporting/">
  <front>
    <title>DMARC Failure Reporting</title>
    <author fullname="Steven M. Jones" initials="S.M." surname="Jones" role="editor">
      <organization>DMARC.org</organization>
    </author>
    <author fullname="Alessandro Vesely" initials="A." surname="Vesely" role="editor">
      <organization>Tana</organization>
    </author>
    <date year="2021" month="February"></date>
  </front>
</reference>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.1035.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3986.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4343.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5234.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5321.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5322.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5890.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6376.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6591.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6651.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6652.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7208.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7489.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8552.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9091.xml"/>
</references>
<references><name>Informative References</name>
<reference anchor="Best-Guess-SPF" target="http://www.openspf.org/FAQ/Best_guess_record">
  <front>
    <title>Sender Policy Framework: Best guess record (FAQ entry)</title>
    <author fullname="S. Kitterman" initials="S." surname="Kitterman"></author>
    <date year="2010" month="May"></date>
  </front>
</reference>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2142.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3464.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4033.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5598.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5617.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6377.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7858.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8020.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8484.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8601.xml"/>
</references>

<section anchor="technology-considerations"><name>Technology Considerations</name>
<t>This section documents some design decisions that were made in the
development of DMARC.  Specifically, addressed here are some
suggestions that were considered but not included in the design.
This text is included to explain why they were considered and not
included in this version.</t>

<section anchor="s-mime"><name>S/MIME</name>
<t>S/MIME, or Secure Multipurpose Internet Mail Extensions, is a
standard for encryption and signing of MIME data in a message.  This
was suggested and considered as a third security protocol for
authenticating the source of a message.</t>
<t>DMARC is focused on authentication at the domain level (i.e., the
Domain Owner taking responsibility for the message), while S/MIME is
really intended for user-to-user authentication and encryption.  This
alone appears to make it a bad fit for DMARC's goals.</t>
<t>S/MIME also suffers from the heavyweight problem of Public Key
Infrastructure, which means that distribution of keys used to verify
signatures needs to be incorporated.  In many instances, this alone
is a showstopper.  There have been consistent promises that PKI
usability and deployment will improve, but these have yet to
materialize.  DMARC can revisit this choice after those barriers are
addressed.</t>
<t>S/MIME has extensive deployment in specific market segments
(government, for example) but does not enjoy similar widespread
deployment over the general Internet, and this shows no signs of
changing.  DKIM and SPF both are deployed widely over the general
Internet, and their adoption rates continue to be positive.</t>
<t>Finally, experiments have shown that including S/MIME support in the
initial version of DMARC would neither cause nor enable a substantial
increase in the accuracy of the overall mechanism.</t>
</section>

<section anchor="method-exclusion"><name>Method Exclusion</name>
<t>It was suggested that DMARC include a mechanism by which a Domain
Owner could tell Message Receivers not to attempt verification by one
of the supported methods (e.g., &quot;check DKIM, but not SPF&quot;).</t>
<t>Specifically, consider a Domain Owner that has deployed one of the
technologies, and that technology fails for some messages, but such
failures don't cause enforcement action.  Deploying DMARC would cause
enforcement action for policies other than &quot;none&quot;, which would appear
to exclude participation by that Domain Owner.</t>
<t>The DMARC development team evaluated the idea of policy exception
mechanisms on several occasions and invariably concluded that there
was not a strong enough use case to include them.  The specific
target audience for DMARC does not appear to have concerns about the
failure modes of one or the other being a barrier to DMARC's
adoption.</t>
<t>In the scenario described above, the Domain Owner has a few options:</t>

<ol>
<li><t>Tighten up its infrastructure to minimize the failure modes of
the single deployed technology.</t>
</li>
<li><t>Deploy the other supported authentication mechanism, to offset
the failure modes of the first.</t>
</li>
<li><t>Deploy DMARC in a reporting-only mode.</t>
</li>
</ol>
</section>

<section anchor="sender-header-field"><name>Sender Header Field</name>
<t>It has been suggested in several message authentication efforts that
the Sender header field be checked for an identifier of interest, as
the standards indicate this as the proper way to indicate a
re-mailing of content such as through a mailing list.  Most recently,
it was a protocol-level option for DomainKeys, but on evolution to
DKIM, this property was removed.</t>
<t>The DMARC development team considered this and decided not to include
support for doing so, for the following reasons:</t>

<ol>
<li><t>The main user protection approach is to be concerned with what
the user sees when a message is rendered.  There is no consistent
behavior among MUAs regarding what to do with the content of the
Sender field, if present.  Accordingly, supporting checking of
the Sender identifier would mean applying policy to an identifier
the end user might never actually see, which can create a vector
for attack against end users by simply forging a Sender field
containing some identifier that DMARC will like.</t>
</li>
<li><t>Although it is certainly true that this is what the Sender field
is for, its use in this way is also unreliable, making it a poor
candidate for inclusion in the DMARC evaluation algorithm.</t>
</li>
<li><t>Allowing multiple ways to discover policy introduces unacceptable
ambiguity into the DMARC evaluation algorithm in terms of which
policy is to be applied and when.</t>
</li>
</ol>
</section>

<section anchor="domain-existence-test"><name>Domain Existence Test</name>
<t>A common practice among MTA operators, and indeed one documented in
<xref target="RFC5617"></xref>, is a test to determine domain existence prior to any more
expensive processing.  This is typically done by querying the DNS for
MX, A, or AAAA resource records for the name being evaluated and
assuming that the domain is nonexistent if it could be determined
that no such records were published for that domain name.</t>
<t>The original pre-standardization version of this protocol included a
mandatory check of this nature.  It was ultimately removed, as the
method's error rate was too high without substantial manual tuning
and heuristic work.  There are indeed use cases this work needs to
address where such a method would return a negative result about a
domain for which reporting is desired, such as a registered domain
name that never sends legitimate mail and thus has none of these
records present in the DNS. The addition of the &quot;np=&quot; tag in this
version of the protocol is one way to address these use cases.</t>
</section>

<section anchor="issues-with-adsp-in-operation"><name>Issues with ADSP in Operation</name>
<t>DMARC has been characterized as a &quot;super-ADSP&quot; of sorts.</t>
<t>Contributors to DMARC have compiled a list of issues associated with
ADSP, gained from operational experience, that have influenced the
direction of DMARC:</t>

<ol>
<li><t>ADSP has no support for subdomains, i.e., the ADSP record for
example.com does not explicitly or implicitly apply to
subdomain.example.com.  If wildcarding is not applied, then
spammers can trivially bypass ADSP by sending from a subdomain
with no ADSP record.</t>
</li>
<li><t>Nonexistent subdomains are explicitly out of scope in ADSP.
There is nothing in ADSP that states receivers should simply
reject mail from NXDOMAINs regardless of ADSP policy (which of
course allows spammers to trivially bypass ADSP by sending email
from nonexistent subdomains).</t>
</li>
<li><t>ADSP has no operational advice on when to look up the ADSP
record.</t>
</li>
<li><t>ADSP has no support for using SPF as an auxiliary mechanism to
DKIM.</t>
</li>
<li><t>ADSP has no support for a slow rollout, i.e., no way to configure
a percentage of email on which the receiver should apply the
policy.  This is important for large-volume senders.</t>
</li>
<li><t>ADSP has no explicit support for an intermediate phase where the
receiver quarantines (e.g., sends to the recipient's &quot;spam&quot;
folder) rather than rejects the email.</t>
</li>
<li><t>The binding between the &quot;From&quot; header domain and DKIM is too
tight for ADSP; they must match exactly.</t>
</li>
</ol>
</section>

<section anchor="organizational-domain-discovery-issues"><name>Organizational Domain Discovery Issues</name>
<t>Although protocols like ADSP are useful for &quot;protecting&quot; a specific
domain name, they are not helpful at protecting subdomains.  If one
wished to protect &quot;example.com&quot; by requiring via ADSP that all mail
bearing an RFC5322.From domain of &quot;example.com&quot; be signed, this would
&quot;protect&quot; that domain; however, one could then craft an email whose
RFC5322.From domain is &quot;security.example.com&quot;, and ADSP would not
provide any protection.  One could use a DNS wildcard, but this can
undesirably interfere with other DNS activity; one could add ADSP
records as fraudulent domains are discovered, but this solution does
not scale and is a purely reactive measure against abuse.</t>
<t>The DNS does not provide a method by which the &quot;domain of record&quot;, or
the domain that was actually registered with a domain registrar, can
be determined given an arbitrary domain name.  Suggestions have been
made that attempt to glean such information from SOA or NS resource
records, but these too are not fully reliable, as the partitioning of
the DNS is not always done at administrative boundaries.</t>
<t>When seeking domain-specific policy based on an arbitrary domain
name, one could &quot;climb the tree&quot;, dropping labels off the left end of
the name until the root is reached or a policy is discovered, but
then one could craft a name that has a large number of nonsense
labels; this would cause a Mail Receiver to attempt a large number of
queries in search of a policy record.  Sending many such messages
constitutes an amplified denial-of-service attack.</t>
<t>The Organizational Domain mechanism is a necessary component to the
goals of DMARC.  The method described in <xref target="determining-the-organizational-domain"></xref> is far from
perfect but serves this purpose reasonably well without adding undue
burden or semantics to the DNS.  If a method is created to do so that
is more reliable and secure than the use of a public suffix list,
DMARC should be amended to use that method as soon as it is generally
available.</t>

<section anchor="public-suffix-lists"><name>Public Suffix Lists</name>
<t>A public suffix list for the purposes of determining the
Organizational Domain can be obtained from various sources.  The most
common one is maintained by the Mozilla Foundation and made public at
<eref target="http://publicsuffix.org">http://publicsuffix.org</eref>.  License terms governing the use of that
list are available at that URI.</t>
<t>Note that if operators use a variety of public suffix lists,
interoperability will be difficult or impossible to guarantee.</t>
</section>
</section>

<section anchor="removal-of-the-pct-tag"><name>Removal of the &quot;pct&quot; Tag</name>
<t>An earlier informational version of the DMARC protocol <xref target="RFC7489"></xref>
included a &quot;pct&quot; tag and specified all integers from 0 to 100 inclusive
as valid values for the tag. The intent of the tag was to provide domain
owners with a method to gradually change their preferred assessment policy
(the p= tag) from 'none' to 'quarantine' or from 'quarantine' to 'reject'
by requesting the stricter treatment for just a percentage of messages
that produced DMARC results of &quot;fail&quot;.</t>
<t>Operational experience and mathematics (specifically the Probability Mass
Function as applied to Binomial Distributions) showed that the pct tag
was usually not accurately applied, unless the value specified was either &quot;0&quot;
or &quot;100&quot; (the default), and the inaccuracies with other values varied widely
from implementation to implementation. The default value was easily implemented,
as it required no special processing on the part of the message receiver, while
the value of &quot;0&quot; took on unintended significance as a value used by some
intermediaries and mailbox providers as an indicator to deviate from
standard handling of the message, usually by rewriting the RFC5322.From
header in an effort to avoid DMARC failures downstream.</t>
<t>These custom actions when the pct= tag was set to &quot;0&quot; proved valuable to the
email community. In particular, header rewriting by an intermediary meant
that a Domain Owner's aggregate reports could reveal to the Domain Owner
how much of its traffic was routing through intermediaries that don't rewrite
the RFC5322.From header. It required work on the part of the Domain Owner to
compare aggregate reports from before and after the p= value was changed
and pct= was included in the DMARC policy record with a value of &quot;0&quot;, but
the data was there. Consequently, knowing how much mail was subject to
possible DMARC failure due to lack of RFC5322.From header rewriting by
intermediaries could assist the Domain Owner in choosing whether or not
to proceed from an applied policy of p=none to p=quarantine or p=reject.
Armed with this knowledge, the Domain Owner could make an informed decision
regarding subjecting its mail traffic to possible DMARC failures based on
the Domain Owner's tolerance for such things.</t>
<t>Because of the value provided by &quot;pct=0&quot; to Domain Owners, it was logical
to keep this functionality in the protocol; at the same time it didn't make
sense to support a tag named &quot;pct&quot; that had only two valid values. This version
of the DMARC protocol therefore introduces the &quot;t&quot; tag as shorthand for &quot;testing&quot;,
with the valid values of &quot;y&quot; and &quot;n&quot;, which are meant to be analogous in their
application by mailbox providers and intermediaries to the &quot;pct&quot; tag values
&quot;0&quot; and &quot;100&quot;, respectively.</t>
</section>
</section>

<section anchor="examples"><name>Examples</name>
<t>This section illustrates both the Domain Owner side and the Mail
Receiver side of a DMARC exchange.</t>

<section anchor="identifier-alignment-examples"><name>Identifier Alignment Examples</name>
<t>The following examples illustrate the DMARC mechanism's use of
Identifier Alignment.  For brevity's sake, only message headers are
shown, as message bodies are not considered when conducting DMARC
checks.</t>

<section anchor="spf"><name>SPF</name>
<t>The following SPF examples assume that SPF produces a passing result.
Alignment cannot exist if SPF does not produce a passing result.</t>
<t>Example 1: SPF in alignment:</t>

<artwork>     MAIL FROM: &lt;sender@example.com&gt;

     From: sender@example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the RFC5321.MailFrom parameter and the RFC5322.From
header field have identical DNS domains.  Thus, the identifiers are in
strict alignment.</t>
<t>Example 2: SPF in alignment (parent):</t>

<artwork>     MAIL FROM: &lt;sender@child.example.com&gt;

     From: sender@example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the RFC5322.From header parameter includes a DNS
domain that is a parent of the RFC5321.MailFrom domain.  Thus, the
identifiers are in relaxed alignment, because they both have the
same Organizational Domain (example.com).</t>
<t>Example 3: SPF not in alignment:</t>

<artwork>     MAIL FROM: &lt;sender@example.net&gt;

     From: sender@child.example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the RFC5321.MailFrom parameter includes a DNS domain
that is neither the same as, a parent of, nor a child of the
RFC5322.From domain.  Thus, the identifiers are not in alignment.</t>
</section>

<section anchor="dkim"><name>DKIM</name>
<t>The examples below assume that the DKIM signatures pass verification.
Alignment cannot exist with a DKIM signature that does not verify.</t>
<t>Example 1: DKIM in alignment:</t>

<artwork>     DKIM-Signature: v=1; ...; d=example.com; ...
     From: sender@example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the DKIM &quot;d=&quot; parameter and the RFC5322.From header field have
identical DNS domains.  Thus, the identifiers are in strict alignment.</t>
<t>Example 2: DKIM in alignment (parent):</t>

<artwork>     DKIM-Signature: v=1; ...; d=example.com; ...
     From: sender@child.example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the DKIM signature's &quot;d=&quot; parameter includes a DNS
domain that is a parent of the RFC5322.From domain.  Thus, the
identifiers are in relaxed alignment, as they have the same
Organizational Domain (example.com).</t>
<t>Example 3: DKIM not in alignment:</t>

<artwork>     DKIM-Signature: v=1; ...; d=sample.net; ...
     From: sender@child.example.com
     Date: Fri, Feb 15 2002 16:54:30 -0800
     To: receiver@example.org
     Subject: here's a sample
</artwork>
<t>In this case, the DKIM signature's &quot;d=&quot; parameter includes a DNS
domain that is neither the same as, a parent of, nor a child of the
RFC5322.From domain.  Thus, the identifiers are not in alignment.</t>
</section>
</section>

<section anchor="domain-owner-example"><name>Domain Owner Example</name>
<t>A Domain Owner that wants to use DMARC should have already deployed
and tested SPF and DKIM.  The next step is to publish a DNS record
that advertises a DMARC policy for the Domain Owner's Organizational
Domain.</t>

<section anchor="entire-domain-monitoring-only"><name>Entire Domain, Monitoring Only</name>
<t>The owner of the domain &quot;example.com&quot; has deployed SPF and DKIM on
its messaging infrastructure.  The owner wishes to begin using DMARC
with a policy that will solicit aggregate feedback from receivers
without affecting how the messages are processed, in order to:</t>

<ul>
<li><t>Confirm that its legitimate messages are authenticating correctly</t>
</li>
<li><t>Verify that all authorized message sources have implemented
authentication measures</t>
</li>
<li><t>Determine how many messages from other sources would be affected
by a blocking policy</t>
</li>
</ul>
<t>The Domain Owner accomplishes this by constructing a policy record
indicating that:</t>

<ul>
<li><t>The version of DMARC being used is &quot;DMARC1&quot; (&quot;v=DMARC1;&quot;)</t>
</li>
<li><t>Receivers should not alter how they treat these messages because
of this DMARC policy record (&quot;p=none&quot;)</t>
</li>
<li><t>Aggregate feedback reports should be sent via email to the address
&quot;dmarc-feedback@example.com&quot;
(&quot;rua=mailto:dmarc-feedback@example.com&quot;)</t>
</li>
<li><t>All messages from this Organizational Domain are subject to this
policy (no &quot;t&quot; tag present, so the default of &quot;n&quot; applies).</t>
</li>
</ul>
<t>The DMARC policy record might look like this when retrieved using a
common command-line tool:</t>

<artwork>  % dig +short TXT _dmarc.example.com.
  &quot;v=DMARC1; p=none; rua=mailto:dmarc-feedback@example.com&quot;
</artwork>
<t>To publish such a record, the DNS administrator for the Domain Owner
creates an entry like the following in the appropriate zone file
(following the conventional zone file format):</t>

<artwork>  ; DMARC record for the domain example.com

  _dmarc  IN TXT ( &quot;v=DMARC1; p=none; &quot;
                   &quot;rua=mailto:dmarc-feedback@example.com&quot; )
</artwork>
</section>

<section anchor="entire-domain-monitoring-only-per-message-reports"><name>Entire Domain, Monitoring Only, Per-Message Reports</name>
<t>The Domain Owner from the previous example has used the aggregate
reporting to discover some messaging systems that had not yet
implemented DKIM correctly, but 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.</t>
<t>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 (<xref target="RFC6591"></xref>) meets the Domain Owner's needs in this scenario.</t>
<t>The Domain Owner accomplishes this by adding the following to its
policy record from <xref target="domain-owner-example"></xref>:</t>

<ul>
<li>Per-message failure reports should be sent via email to the
address &quot;auth-reports@example.com&quot;
(&quot;ruf=mailto:auth-reports@example.com&quot;)</li>
</ul>
<t>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):</t>

<artwork>  % dig +short TXT _dmarc.example.com.
  &quot;v=DMARC1; p=none; rua=mailto:dmarc-feedback@example.com;
   ruf=mailto:auth-reports@example.com&quot;
</artwork>
<t>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):</t>

<artwork>  ; DMARC record for the domain example.com

  _dmarc  IN TXT ( &quot;v=DMARC1; p=none; &quot;
                    &quot;rua=mailto:dmarc-feedback@example.com; &quot;
                    &quot;ruf=mailto:auth-reports@example.com&quot; )
</artwork>
</section>

<section anchor="per-message-failure-reports-directed-to-third-party"><name>Per-Message Failure Reports Directed to Third Party</name>
<t>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
verify that the third party wishes to receive the failure reports
for this domain.</t>
<t>The Domain Owner needs to alter its policy record from <xref target="entire-domain-monitoring-only-per-message-reports"></xref>
as follows:</t>

<ul>
<li>Per-message failure reports should be sent via email to the
address &quot;auth-reports@thirdparty.example.net&quot;
(&quot;ruf=mailto:auth-reports@thirdparty.example.net&quot;)</li>
</ul>
<t>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):</t>

<artwork>  % dig +short TXT _dmarc.example.com.
  &quot;v=DMARC1; p=none; rua=mailto:dmarc-feedback@example.com;
   ruf=mailto:auth-reports@thirdparty.example.net&quot;
</artwork>
<t>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):</t>

<artwork>  ; DMARC record for the domain example.com

  _dmarc IN TXT ( &quot;v=DMARC1; p=none; &quot;
                  &quot;rua=mailto:dmarc-feedback@example.com; &quot;
                  &quot;ruf=mailto:auth-reports@thirdparty.example.net&quot; )
</artwork>
<t>Because the address used in the &quot;ruf&quot; tag is outside the
Organizational Domain in which this record is published, conforming
Receivers will implement additional checks as described in Section 3 of
<xref target="DMARC-Aggregate-Reporting"></xref>.  In order to pass these additional
checks, the third party will need to publish an additional DNS record
as follows:</t>

<ul>
<li>Given the DMARC record published by the Domain Owner at
&quot;_dmarc.example.com&quot;, the DNS administrator for the third party
will need to publish a TXT resource record at
&quot;example.com._report._dmarc.thirdparty.example.net&quot; with the value
&quot;v=DMARC1;&quot;.</li>
</ul>
<t>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):</t>

<artwork>  % dig +short TXT example.com._report._dmarc.thirdparty.example.net
  &quot;v=DMARC1;&quot;
</artwork>
<t>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):</t>

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

  example.com._report._dmarc   IN   TXT    &quot;v=DMARC1;&quot;
</artwork>
<t>Mediators and other third parties should refer to Section 3 of <xref target="DMARC-Aggregate-Reporting"></xref>
for the full details of this mechanism.</t>
</section>

<section anchor="subdomain-sampling-and-multiple-aggregate-report-uris"><name>Subdomain, Testing, and Multiple Aggregate Report URIs</name>
<t>The Domain Owner has implemented SPF and DKIM in a subdomain used for
pre-production testing of messaging services.  It now wishes to express
a severity of concern for messages from this subdomain that fail to
authenticate to indicate to participating receivers that use of this
domain is not valid.</t>
<t>As a first step, it will express that it considers to be suspicious
messages using this subdomain that fail authentication. The goal here
will be to enable examination of messages sent to mailboxes hosted by
participating receivers as method for troubleshooting any existing
authentication issues.  Aggregate feedback reports will be sent to
a mailbox within the Organizational Domain, and to a mailbox at a third
party selected and authorized to receive same by the Domain Owner.</t>
<t>The Domain Owner will accomplish this by constructing a policy record
indicating that:</t>

<ul>
<li><t>The version of DMARC being used is &quot;DMARC1&quot; (&quot;v=DMARC1;&quot;)</t>
</li>
<li><t>It is applied only to this subdomain (record is published at
&quot;_dmarc.test.example.com&quot; and not &quot;_dmarc.example.com&quot;)</t>
</li>
<li><t>Receivers are advised that the Domain Owner considers messages
that fail to authenticate to be suspicious (&quot;p=quarantine&quot;)</t>
</li>
<li><t>Aggregate feedback reports should be sent via email to the
addresses &quot;dmarc-feedback@example.com&quot; and
&quot;example-tld-test@thirdparty.example.net&quot;
(&quot;rua=mailto:dmarc-feedback@example.com,
 mailto:tld-test@thirdparty.example.net&quot;)</t>
</li>
<li><t>The Domain Owner desires only that an actor performing a DMARC
verification check apply any special handling rules it might have
in place, such as rewriting the RFC53322.From header; the Domain
Owner is testing its setup at this point, and so does not want
the handling policy to be applied. (&quot;t=y&quot;)</t>
</li>
</ul>
<t>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):</t>

<artwork>  % dig +short TXT _dmarc.test.example.com
  &quot;v=DMARC1; p=quarantine; rua=mailto:dmarc-feedback@example.com,
   mailto:tld-test@thirdparty.example.net t=y&quot;
</artwork>
<t>To publish such a record, the DNS administrator for the Domain Owner
might create an entry like the following in the appropriate zone
file:</t>

<artwork>  ; DMARC record for the domain test.example.com

  _dmarc IN  TXT  ( &quot;v=DMARC1; p=quarantine; &quot;
                    &quot;rua=mailto:dmarc-feedback@example.com,&quot;
                    &quot;mailto:tld-test@thirdparty.example.net;&quot;
                    &quot;t=y&quot; )
</artwork>
<t>Once enough time has passed to allow for collecting enough reports to
give the Domain Owner confidence that all legitimate email sent using
the subdomain is properly authenticating and passing DMARC checks, then
the Domain Owner can update the policy record to indicate that it considers
authentication failures to be a clear indication that use of the subdomain
is not valid. It would do this by altering the DNS record to advise
receivers of its position on such messages (&quot;p=reject&quot;).</t>
<t>After alteration, 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):</t>

<artwork>  % dig +short TXT _dmarc.test.example.com
  &quot;v=DMARC1; p=reject; rua=mailto:dmarc-feedback@example.com,
   mailto:tld-test@thirdparty.example.net&quot;
</artwork>
<t>To publish such a record, the DNS administrator for the Domain Owner
might create an entry like the following in the appropriate zone
file:</t>

<artwork>  ; DMARC record for the domain test.example.com

  _dmarc IN  TXT  ( &quot;v=DMARC1; p=reject; &quot;
                    &quot;rua=mailto:dmarc-feedback@example.com,&quot;
                    &quot;mailto:tld-test@thirdparty.example.net&quot; )
</artwork>
</section>
</section>

<section anchor="mail-receiver-example"><name>Mail Receiver Example</name>
<t>A Mail Receiver that wants to use DMARC should already be checking
SPF and DKIM, and possess the ability to collect relevant information
from various email-processing stages to provide feedback to Domain
Owners (possibly via Report Receivers).</t>
</section>

<section anchor="processing-of-smtp-time"><name>Processing of SMTP Time</name>
<t>An optimal DMARC-enabled Mail Receiver performs authentication and
Identifier Alignment checking during the SMTP <xref target="RFC5321"></xref> conversation.</t>
<t>Prior to returning a final reply to the DATA command, the Mail
Receiver's MTA has performed:</t>

<ol>
<li><t>An SPF check to determine an SPF-authenticated Identifier.</t>
</li>
<li><t>DKIM checks that yield one or more DKIM-authenticated
Identifiers.</t>
</li>
<li><t>A DMARC policy lookup.</t>
</li>
</ol>
<t>The presence of an Author Domain DMARC record indicates that the Mail
Receiver should continue with DMARC-specific processing before
returning a reply to the DATA command.</t>
<t>Given a DMARC record and the set of Authenticated Identifiers, the
Mail Receiver checks to see if the Authenticated Identifiers align
with the Author Domain (taking into consideration any strict versus
relaxed options found in the DMARC record).</t>
<t>For example, the following sample data is considered to be from a
piece of email originating from the Domain Owner of &quot;example.com&quot;:</t>

<artwork>  Author Domain: example.com
  SPF-authenticated Identifier: mail.example.com
  DKIM-authenticated Identifier: example.com
  DMARC record:
    &quot;v=DMARC1; p=reject; aspf=r; 
     rua=mailto:dmarc-feedback@example.com&quot;
</artwork>
<t>In the above sample, both the SPF-authenticated Identifier and the
DKIM-authenticated Identifier align with the Author Domain.  The Mail
Receiver considers the above email to pass the DMARC check, avoiding
the &quot;reject&quot; policy that is requested to be applied to email that fails
to pass the DMARC check.</t>
<t>If no Authenticated Identifiers align with the Author Domain, then
the Mail Receiver applies the DMARC-record-specified policy.
However, before this action is taken, the Mail Receiver can consult
external information to override the Domain Owner's Assessment Policy.<br />
For example, if the Mail Receiver knows that this particular email
came from a known and trusted forwarder (that happens to break both
SPF and DKIM), then the Mail Receiver may choose to ignore the Domain
Owner's policy.</t>
<t>The Mail Receiver is now ready to reply to the DATA command.  If the
DMARC check yields that the message is to be rejected, then the Mail
Receiver replies with a 5xy code to inform the sender of failure.  If
the DMARC check cannot be resolved due to transient network errors,
then the Mail Receiver replies with a 4xy code to inform the sender
as to the need to reattempt delivery later.  If the DMARC check
yields a passing message, then the Mail Receiver continues on with
email processing, perhaps using the result of the DMARC check as an
input to additional processing modules such as a domain reputation
query.</t>
<t>Before exiting DMARC-specific processing, the Mail Receiver checks to
see if the Author Domain DMARC record requests AFRF-based reporting.
If so, then the Mail Receiver can emit an AFRF to the reporting
address supplied in the DMARC record.</t>
<t>At the exit of DMARC-specific processing, the Mail Receiver captures
(through logging or direct insertion into a data store) the result of
DMARC processing.  Captured information is used to build feedback for
Domain Owner consumption.  This is not necessary if the Domain Owner
has not requested aggregate reports, i.e., no &quot;rua&quot; tag was found in
the policy record.</t>
</section>

<section anchor="utilization-of-aggregate-feedback-example"><name>Utilization of Aggregate Feedback: Example</name>
<t>Aggregate feedback is consumed by Domain Owners to verify their
understanding of how a given domain is being processed by the Mail
Receiver.  Aggregate reporting data on emails that pass all
DMARC-supporting authentication checks is used by Domain Owners to
verify that their authentication practices remain accurate.  For
example, if a third party is sending on behalf of a Domain Owner,
the Domain Owner can use aggregate report data to verify ongoing
authentication practices of the third party.</t>
<t>Data on email that only partially passes underlying authentication
checks provides visibility into problems that need to be addressed by
the Domain Owner.  For example, if either SPF or DKIM fails to pass,
the Domain Owner is provided with enough information to either
directly correct the problem or understand where authentication-
breaking changes are being introduced in the email transmission path.
If authentication-breaking changes due to email transmission path
cannot be directly corrected, then the Domain Owner at least
maintains an understanding of the effect of DMARC-based policies upon
the Domain Owner's email.</t>
<t>Data on email that fails all underlying authentication checks
provides baseline visibility on how the Domain Owner's domain is
being received at the Mail Receiver.  Based on this visibility, the
Domain Owner can begin deployment of authentication technologies
across uncovered email sources, if the mail that is failing the checks
was generated by or on behalf of the Domain Owner.  Data regarding
failing authentication checks can also allow the Domain Owner to
come to an understanding of how its domain is being misused.</t>
<t>(Aggregate report example should be moved to <xref target="DMARC-Aggregate-Reporting"></xref>)</t>
</section>
</section>

<section anchor="change-log"><name>Change Log</name>

<section anchor="january-5-2021"><name>January 5, 2021</name>

<section anchor="ticket-80-dmarcbis-should-have-clear-and-concise-defintion-of-dmarc"><name>Ticket 80 - DMARCbis SHould Have Clear and Concise Defintion of DMARC</name>

<ul>
<li>Updated text for Abstract and Introduction sections.</li>
<li>Diffs are recorded here - <eref target="https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/1/files">https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/1/files</eref></li>
</ul>
</section>
</section>

<section anchor="february-4-2021"><name>February 4, 2021</name>

<section anchor="ticket-1-spf-rfc-4408-vs-7208"><name>Ticket 1 - SPF RFC 4408 vs 7208</name>

<ul>
<li>Some rearranging of text in the &quot;SPF-Authenticated Identifiers&quot; section</li>
<li>Clarification of the term &quot;in alignment&quot; in that same section</li>
<li>Diffs are here - <eref target="https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/3/files">https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/3/files</eref></li>
</ul>
</section>
</section>

<section anchor="february-10-2021"><name>February 10, 2021</name>

<section anchor="ticket-84-remove-erroneous-references-to-rfc3986"><name>Ticket 84 - Remove Erroneous References to RFC3986</name>

<ul>
<li>Several references to RFC3986 changed to RFC7208</li>
<li>Diffs are here - <eref target="https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/4/files">https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/4/files</eref></li>
</ul>
</section>
</section>

<section anchor="march-1-2021"><name>March 1, 2021</name>

<section anchor="design-team-work-begins"><name>Design Team Work Begins</name>

<ul>
<li>Added change log section to document</li>
</ul>
</section>
</section>

<section anchor="march-8-2021"><name>March 8, 2021</name>

<section anchor="removed-e-gustafsson-as-editor"><name>Removed E. Gustafsson as editor</name>

<ul>
<li>He withdrew as editor after a job change.</li>
</ul>
</section>

<section anchor="ticket-3-two-tiny-nits"><name>Ticket 3 - Two tiny nits</name>

<ul>
<li>Changes to wording in section 6.6.2, Determine Handling Policy, steps
3 and 4.</li>
<li>New text documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/3#comment:6">https://trac.ietf.org/trac/dmarc/ticket/3#comment:6</eref></li>
<li>No change to section 6.6.3, Policy Discovery; ticket seems to pre-date
current text, which appears to have answered the concern raised.</li>
</ul>
</section>

<section anchor="ticket-4-definition-of-fo-parameter"><name>Ticket 4 - Definition of &quot;fo&quot; parameter</name>

<ul>
<li>Changes to wording in section 6.3, to bring clarity to use of colon-separated
list as possible value to &quot;fo&quot;</li>
<li>New text documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/4#comment:4">https://trac.ietf.org/trac/dmarc/ticket/4#comment:4</eref></li>
</ul>
</section>
</section>

<section anchor="march-16-2021"><name>March 16, 2021</name>

<section anchor="ticket-7-abnf-for-dmarc-record-is-slightly-wrong"><name>Ticket 7 - ABNF for dmarc-record is slightly wrong</name>

<ul>
<li>New text documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/7">https://trac.ietf.org/trac/dmarc/ticket/7</eref></li>
</ul>
</section>

<section anchor="ticket-26-abnf-for-pct-allows-999"><name>Ticket 26 - ABNF for pct allows &quot;999&quot;</name>

<ul>
<li>Updated ABNF for dmarc-percent</li>
<li>New text documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/26#comment:6">https://trac.ietf.org/trac/dmarc/ticket/26#comment:6</eref></li>
<li>Ticket 47, Remove pct= tag, rendered change obsolete</li>
</ul>
</section>
</section>

<section anchor="march-23-2021"><name>March 23, 2021</name>

<section anchor="ticket-75-using-wording-alternatives-to-disposition-dispose-and-the-like"><name>Ticket 75 - Using wording alternatives to 'disposition', 'dispose', and the like</name>

<ul>
<li>Changed disposition/dispose to &quot;handling&quot;</li>
<li>Diffs documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/75#comment:3">https://trac.ietf.org/trac/dmarc/ticket/75#comment:3</eref></li>
</ul>
</section>

<section anchor="ticket-72-remove-absolute-requirement-for-p-tag-in-dmarc-record"><name>Ticket 72 - Remove absolute requirement for p= tag in DMARC record</name>

<ul>
<li>Changed from REQUIRED to RECOMMENDED, noted default with forward reference to discussion</li>
<li>Diffs documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/72#comment:3">https://trac.ietf.org/trac/dmarc/ticket/72#comment:3</eref></li>
</ul>
</section>
</section>

<section anchor="march-29-2021"><name>March 29, 2021</name>

<section anchor="ticket-54-remove-or-expand-limits-on-number-of-recipients-per-report"><name>Ticket 54 - Remove or expand limits on number of recipients per report</name>

<ul>
<li>Removed limit</li>
<li>Diffs documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/54#comment:5">https://trac.ietf.org/trac/dmarc/ticket/54#comment:5</eref></li>
</ul>
</section>
</section>

<section anchor="april-12-2021"><name>April 12, 2021</name>

<section anchor="ticket-50-remove-ri-tag"><name>Ticket 50 - Remove ri= tag</name>

<ul>
<li>Updated text to recommend against its usage, a la the ptr mechanism in RFC 7208</li>
<li>Diffs documented here - <eref target="https://trac.ietf.org/trac/dmarc/ticket/50#comment:5">https://trac.ietf.org/trac/dmarc/ticket/50#comment:5</eref></li>
</ul>
</section>

<section anchor="ticket-66-define-what-it-means-to-have-implemented-dmarc"><name>Ticket 66 - Define what it means to have implemented DMARC</name>

<ul>
<li>Proposed new text (taken straight from <eref target="https://trac.ietf.org/trac/dmarc/ticket/66">https://trac.ietf.org/trac/dmarc/ticket/66</eref>
as replacement for current text in &quot;Minimum Implemenatations&quot;</li>
</ul>
</section>

<section anchor="ticket-96-tweaks-to-abstract-and-introduction"><name>Ticket 96 - Tweaks to Abstract and Introduction</name>

<ul>
<li>Changed phrase in Abstract to &quot;an email author's domain name&quot;</li>
<li>Changed phrase in Introduction to &quot;reports about email use of the domain name&quot;</li>
</ul>
</section>
</section>

<section anchor="april-13-2021"><name>April 13, 2021</name>

<section anchor="ticket-53-remove-reporting-message-size-chunking"><name>Ticket 53 - Remove reporting message size chunking</name>

<ul>
<li>Proposed text to remove all references to message size chunking</li>
<li>Data demonstrating lack of use of feature entered into ticket -
<eref target="https://trac.ietf.org/trac/dmarc/ticket/53#comment:4">https://trac.ietf.org/trac/dmarc/ticket/53#comment:4</eref></li>
</ul>
</section>

<section anchor="ticket-52-remove-strict-alignment-and-adkim-and-aspf-tags"><name>Ticket 52 - Remove strict alignment (and adkim and aspf tags)</name>

<ul>
<li>Proposed text to remove all references to strict alignment</li>
<li>Data demonstrating lack of use of feature entered into ticket -
<eref target="https://trac.ietf.org/trac/dmarc/ticket/52#comment:2">https://trac.ietf.org/trac/dmarc/ticket/52#comment:2</eref></li>
</ul>
</section>

<section anchor="ticket-47-remove-pct-tag"><name>Ticket 47 - Remove pct= tag</name>

<ul>
<li>Proposed text to remove all references to pct and message sampling</li>
<li>Data demonstrating lack of use of feature entered into ticket -
<eref target="https://trac.ietf.org/trac/dmarc/ticket/47#comment:4">https://trac.ietf.org/trac/dmarc/ticket/47#comment:4</eref></li>
</ul>
</section>

<section anchor="ticket-2-flow-of-operations-text-in-dmarc-base"><name>Ticket 2 - Flow of operations text in dmarc-base</name>

<ul>
<li>Update ASCII Art</li>
<li>Proposed text to replace description of ASCII Art</li>
<li>Proposed text to update Domain Owner Actions section</li>
</ul>
</section>
</section>

<section anchor="april-14-2021"><name>April 14, 2021</name>

<section anchor="ticket-107-dmarcbis-should-take-a-stand-on-multi-valued-from-fields"><name>Ticket 107 - DMARCbis should take a stand on multi-valued From fields</name>

<ul>
<li>Proposed text that limits processing to only those times when all domains
are the same.</li>
</ul>
</section>

<section anchor="ticket-82-deprecate-rf-and-maybe-fo-tag"><name>Ticket 82 - Deprecate rf= and maybe fo= tag</name>

<ul>
<li>Proposed text to deprecate rf= tag, while leaving fo= tag as is</li>
</ul>
</section>

<section anchor="ticket-85-proposed-change-to-wording-describing-p-tag-and-values"><name>Ticket 85 - Proposed change to wording describing 'p' tag and values</name>

<ul>
<li>The language expressing the semantics is proposed to be changed to be,
in a sense, egocentric. How do I, the domain owner feel about (assess)
the meaning of a DMARC failure?</li>
</ul>
</section>
</section>

<section anchor="april-15-2021"><name>April 15, 2021</name>

<section anchor="ticket-86-a-r-results-for-dmarc"><name>Ticket 86 - A-R results for DMARC</name>

<ul>
<li>Proposed text to add for polrec.p and polrec.domain methods for registry
update.</li>
<li>Did not include polrec.pct due to proposal to remove pct tag (Ticket 47)</li>
</ul>
</section>

<section anchor="ticket-62-make-aggregate-reporting-a-normative-must"><name>Ticket 62 - Make aggregate reporting a normative MUST</name>

<ul>
<li>Proposed text to do just that in Mail Receiver Actions, section
titled &quot;Send Aggregate Reports&quot;</li>
</ul>
</section>
</section>

<section anchor="april-19-2021"><name>April 19, 2021</name>

<section anchor="ticket-109-sanity-check-dmarcbis-document"><name>Ticket 109 - Sanity Check DMARCbis Document</name>

<ul>
<li>Updated document to remove all &quot;original text&quot;/&quot;proposed text&quot; couplets
in favor of one (hopefully coherent) document full of proposed text
changes.</li>
<li>Noted which tickets were the cause of whatever rfcdiff output will show
in tracker</li>
</ul>
</section>
</section>

<section anchor="april-20-2021"><name>April 20, 2021</name>

<section anchor="ticket-108-changes-to-dmarcbis-for-psd"><name>Ticket 108 - Changes to DMARCbis for PSD</name>

<ul>
<li>Incorporating requests for changes to DMARCbis made in text of
&quot;Experimental DMARC Extension for Public Suffix Domains&quot;
(<eref target="https://datatracker.ietf.org/doc/draft-ietf-dmarc-psd/">https://datatracker.ietf.org/doc/draft-ietf-dmarc-psd/</eref>)</li>
</ul>
</section>
</section>

<section anchor="april-22-2021"><name>April 22, 2021</name>

<section anchor="ticket-104-update-the-security-considerations-section-11-3-on-dns"><name>Ticket 104 - Update the Security Considerations section 11.3 on DNS</name>

<ul>
<li>Updated text. Diffs are here - <eref target="https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/31/files">https://github.com/ietf-wg-dmarc/draft-ietf-dmarc-dmarcbis/pull/31/files</eref></li>
</ul>
</section>
</section>

<section anchor="june-16-2021"><name>June 16, 2021</name>

<section anchor="publication-of-draft-ietf-dmarc-dmarcbis-02"><name>Publication of draft-ietf-dmarc-dmarcbis-02</name>

<ul>
<li>Includes final resolution for tickets 4, 47, 50, 52, 53, 54, and 82</li>
</ul>
</section>
</section>

<section anchor="august-12-2021"><name>August 12, 2021</name>

<section anchor="publication-of-draft-ietf-dmarc-dmarcbis-03"><name>Publication of draft-ietf-dmarc-dmarcbis-03</name>

<ul>
<li>Removal of &quot;pct&quot; tag</li>
<li>Addition of &quot;t&quot; tag</li>
<li>Rearranging of some text and formatting for better readability and consistency.</li>
</ul>
</section>
</section>
</section>

<section anchor="acknowledgements" numbered="false"><name>Acknowledgements</name>
<t>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 <eref target="http://dmarc.org">http://dmarc.org</eref>).
Participating companies included Agari, American Greetings, AOL, Bank
of America, Cloudmark, Comcast, Facebook, Fidelity Investments,
Google, JPMorgan Chase &amp; 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.</t>
<t>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.</t>
</section>

</back>

</rfc>