Domain-based Message Authentication, Reporting & Conformance
Domain-based Message Authentication, Reporting & Conformance WG
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Domain-based Message Authentication, Reporting & Conformance (DMARC)
uses existing mail authentication technologies (SPF and DKIM) to
extend validation to the RFC5322.From field. DMARC uses DNS records
to add policy-related requests for receivers and defines a feedback
mechanism from receivers back to domain owners. This allows a domain
owner to advertise that mail can safely receive differential
handling, such as rejection, when the use of the domain name in the
From field is not authenticated. Existing deployment of DMARC has
demonstrated utility at internet scale, in dealing with significant
email abuse, and has permitted simplifying some mail handling
processes. However, DMARC is problematic for mail that does not flow
from operators having a relationship with the domain owner, directly
to receivers operating the destination mailbox (for example, mailing
lists, publish-to-friend functionality, mailbox forwarding via
".forward", and third-party services that send on behalf of clients).
The working group will explore possible updates and extensions to the
specifications in order to address limitations and/or add
capabilities. It will also provide technical implementation guidance
and review possible enhancements elsewhere in the mail handling
sequence that could improve DMARC compatibility.
The existing DMARC base specification is published as Informational
RFC 7489 in the Independent Stream.
Specifications produced by the working group will ensure preservation
of DMARC utility for detecting unauthorized use of domain names,
while improving the identification of legitimate sources that do not
currently conform to DMARC requirements. Issues based on operational
experience and/or data aggregated from multiple sources will be given
The working group will seek to preserve interoperability with the
installed base of DMARC systems, and provide detailed justification
for any non-interoperability. As the working group develops solutions
to deal with indirect mail flows, it will seek to maintain the
end-to-end nature of existing identifier fields in mail, in
particular avoiding solutions that require rewriting of originator
Working group activities will pursue four tracks:
1. Addressing the issues with indirect mail flows
The working group will specify mechanisms for reducing or eliminating
the DMARC's effects on indirect mail flows, including deployed
behaviors of many different intermediaries, such as mailing list
managers, automated mailbox forwarding services, and MTAs that
perform enhanced message handling that results in message
modification. Among the choices for addressing these issues are:
- A form of DKIM signature that is better able to survive transit
- Collaborative or passive transitive mechanisms that enable an
intermediary to participate in the trust sequence, propagating
authentication directly or reporting its results.
- Message modification by an intermediary, to avoid authentication
failures, such as by using specified conventions for changing
the aligned identity.
Consideration also will be given to survivable authentication through
sequences of multiple intermediaries.
2. Reviewing and improving the base DMARC specification
The working group will not develop additional mail authentication
technologies, but may document desirable uses of existing authentication
The base specification relies on the ability of an email receiver to
determine the organizational domain responsible for sending mail. An
organizational domain is the 'base' name that is allocated from a
public registry; examples of registries include ".com" or ".co.uk".
While the common practice is to use a "public suffix" list to
determine organizational domain, it is widely recognized that this
solution will not scale, and that the current list often is
inaccurate. The task of defining a standard mechanism for identifying
organizational domain is out of scope for this working group. However
the working group can consider extending the base DMARC specification
to accommodate such a standard, should it be developed during the
life of this working group.
Improvements in DMARC features (identifier alignment, reporting,
policy preferences) will be considered, such as:
- Enumeration of data elements required in "Failure" reports
(specifically to address privacy issues)
- Handling potential reporting abuse
- Aggregate reporting to support additional reporting scenarios
- Alternate reporting channels
- Utility of arbitrary identifier alignment
- Utility of a formalized policy exception mechanism
3. DMARC Usage
The working group will document operational practices in terms of
configuration, installation, monitoring, diagnosis and reporting. It
will catalog currently prevailing guidelines as well as developing
advice on practices that are not yet well-established but which are
believed to be appropriate.
The group will consider separating configuration and other deployment
information that needs to be in the base spec, from information that
should be in a separate guide.
Among the topics anticipated to be included in the document are:
- Identifier alignment configuration options
- Implementation decisions regarding "pct"
- Determining effective RUA sending frequency
- Leveraging policy caching
- Various options for integrating within an existing flow
- Defining a useful, common set of options for the addresses to
which feedback reports are to be sent
- When and how to use local policy override options
4. Related work
Extensions to SPF/DKIM/DMARC that do not already fit under
the charter of any existing working group can be considered for adoption
by DMARC Working Group after consultation with the responsible AD.
A prime example is draft-levine-appsarea-eaiauth, which provides EAI-related
updates to DMARC and the protocols upon which it depends.
Any such work needs to carefully consider interoperability implications.
Draft description of interoperability issues for indirect mail
flows and plausible methods for reducing them. This is now
complete and published as RFC 7960.
Specification of DMARC improvements to support indirect mail flows;
this is now complete as draft-ietf-dmarc-arc-protocol (ARC).
Draft Guide on DMARC Usage.
Review and refinement of the DMARC specification.
Completion of Guide on DMARC and ARC Usage.
DMARC - http://dmarc.org
SPF - RFC7208
Authentication-Results Header Field - RFC7001
DKIM - RFC6376
Internet Message Format - RFC5322
OAR / Original Authentication Results -
Using DMARC - draft-crocker-dmarc-bcp-03
Delegating DKIM Signing Authority - draft-kucherawy-dkim-delegate-00
DKIM Third-Party Authorization Label - draft-otis-dkim-tpa-label-03