Network Working Group                                       S. Kitterman
Internet-Draft                                    fTLD Registry Services
Updates: 7489 (if approved)                            November 21, 2018                             January 14, 2019
Intended status: Informational
Expires: May 25, July 18, 2019

DMARC (Domain-based Message Authentication, Reporting, and Conformance)
               Extension For PSDs (Public Suffix Domains)


   DMARC (Domain-based Message Authentication, Reporting, and
   Conformance) is a scalable mechanism by which a mail-originating
   organization can express domain-level policies and preferences for
   message validation, disposition, and reporting, that a mail-receiving
   organization can use to improve mail handling.  DMARC policies can be
   applied at the individual domain level or for a set of domains at the
   organizational level.  The design of DMARC precludes grouping
   policies for a set of domains above the organizational level, such as
   TLDs (Top Level Domains).  These types of domains (which are not all
   at the top level of the DNS tree) can be collectively referred to as
   Public Suffix Domains (PSDs).  For the subset of PSDs that require
   DMARC usage, this memo describes an extension to DMARC to enable
   DMARC functionality for such domains.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 25, July 18, 2019.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Definitions . . . . . . . . . . . . . . . . .   4
     2.1.  Conventions Used in This Document . . . . . . . . . . . .   4
     2.2.  Public Suffix Domain (PSD)  . . . . . . . . . . . . . . .   4
     2.3.  Longest PSD . . . . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Public Suffix Operator (PSO)  . . . . . . . . . . . . . .   4
     2.5.  PSO Controlled Domain Names . . . . . . . . . . . . . . .   5
     2.6.  Non-existent Domains  . . . . . . . . . . . . . . . . . .   5
   3.  PSD DMARC Updates to DMARC Requirements . . . . . . . . . . .   5
     3.1.  General Updates . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Section 6.1 DMARC Policy Record . . . . . . . . . . . . .   5
     3.3.  Section 6.5.  Domain Owner Actions  . . . . . . . . . . .   5
     3.4.  Section 6.6.3.  Policy Discovery  . . . . . . . . . . . .   5
     3.5.  Section 7.  DMARC Feedback  . . . . . . . . . . . . . . .   6
   4.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   6
     4.1.  Feedback leakage  . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  DMARC Public Suffix Domain (PSD)                 Registry   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9   8

1.  Introduction

   DMARC [RFC7489] provides a mechanism for publishing organizational
   policy information to email receivers.  DMARC [RFC7489] allows policy
   to be specified for both individual domains and sets of domains
   within a single organization.  For domains above the organizational
   level in the DNS tree, policy can only be published for the exact
   domain.  There is no method available to such domains to express
   lower level policy or receive feedback reporting for sets of domains.
   This prevents policy application to non-existent domains and
   identification of domain abuse in email, which can be important for
   brand and consumer protection.

   As an example, imagine a country code TLD (ccTLD) which has public
   subdomains for government and commercial use (.gov.example and
   .com.example).  Within the .gov.example public suffix, use of DMARC
   [RFC7489] has been mandated and .gov.example has published its own
   DMARC [RFC7489] record:



   This would provide policy and feedback for mail sent from
   @gov.example, but not and there is no way to publish
   an organizational level policy that would do so.  While, in theory,
   receivers could reject mail from non-existent domains, not all
   receivers do so.  Non-existence of the sending domain can be a factor
   in a mail delivery decision, but is not generally treated as
   definitive on its own.

   This memo provides a simple extension to DMARC [RFC7489] to allow
   operators of Public Suffix Domains (PSDs) to express policy for
   groups of subdomains, extends the DMARC [RFC7489] policy query
   functionality to detect and process such a policy, describes receiver
   feedback for such policies, and provides controls to mitigate
   potential privacy considerations associated with this extension.

   There are two types of Public Suffix Operators (PSOs) for which this
   extension would be useful and appropriate:

   o  Branded PSDs (e.g., ".google"): These domains are effectively
      Organizational Domains as discussed in DMARC [RFC7489].  They
      control all subdomains of the tree.  These are effectively private
      domains, but listed in the Public Suffix List.  They are treated
      as Public for DMARC [RFC7489] purposes.  They require the same
      protections as DMARC [RFC7489] Organizational Domains, but are
      currently excluded.

   o  Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
      Because existing Organizational Domains using this PSD have their
      own DMARC policy, the applicability of this extension is for non-
      existent domains.  The extension allows the brand protection
      benefits of DMARC [RFC7489] to extend to the entire PSD, including
      cousin domains of registered organizations.

   Due to the design of DMARC [RFC7489] and the nature of the Internet
   email architecture [RFC5598], there are interoperability issues
   associated with DMARC [RFC7489] deployment.  These are discussed in
   Interoperability Issues between DMARC and Indirect Email Flows
   [RFC7960].  These issues are not applicable to PSDs, since they
   (e.g., the ".gov.example" used above) do not send mail.

   DMARC [RFC7489], by design, does not support usage by PSD operators. PSOs.  For PSDs
   that require use of DMARC [RFC7489], an extension of DMARC reporting
   and enforcement capability is needed for PSD operators PSO to effectively manage
   and monitor implementation of PSD requirements.

2.  Terminology and Definitions

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

2.1.  Conventions Used in This Document

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

2.2.  Public Suffix Domain (PSD)

   The global Internet Domain Name System (DNS) is documented in
   numerous Requests for Comment (RFC).  It defines a tree of names
   starting with root, ".", immediately below which are Top Level Domain
   names such as ".com" and ".us".  They are not available for private
   registration.  In many cases the public portion of the DNS tree is
   more than one level deep.  PSD DMARC includes all public domains
   above the organizational level in the tree, e.g., "".

2.3.  Longest PSD

   Organizational Domain (DMARC [RFC7489] Section 3.2) with one label

2.4.  Public Suffix Operator (PSO)

   A Public Suffix Operator manages operations within their PSD.

2.5.  PSO Controlled Domain Names

   PSO Controlled Domain Names are names in the DNS that are managed by
   a PSO and are not available for use as Organizational Domains (the
   term Organizational Domains is defined in DMARC [RFC7489]
   Section 3.2).  Depending on PSD policy, these will have one (e.g.,
   ".com") or more (e.g., "") name components.

2.6.  Non-existent Domains

   For DMARC [RFC7489] purposes, a non-existent domain is a domain name
   that publishes none of A, AAAA, or MX records that the receiver is
   willing to accept.  This is a broader definition than that in
   NXDOMAIN [RFC8020].

3.  PSD DMARC Updates to DMARC Requirements

   This document updates DMARC [RFC7489] as follows:

3.1.  General Updates

   References to "Domain Owners" also apply to PSOs.

3.2.  Section 6.1 DMARC Policy Record

   PSD DMARC records are published as a subdomain of the PSD.  For the
   PSD ".example", the PSO would post DMARC policy in a TXT record at

3.3.  Section 6.5.  Domain Owner Actions

   In addition to the DMARC [RFC7489] domain owner actions, PSOs will
   need that
   require use of DMARC ought to update the "DMARC Public Suffix Domain (PSD) Registry".  This
   registry is defined in Section 6.1. make that information available to

3.4.  Section 6.6.3.  Policy Discovery

   A new step between step 3 and 4 is added:

   3A.  If the set is now empty and the longest PSD (Section 2.3) of the
      Organizational Domain is listed in one that the DMARC receiver has determined is
      acceptable for PSD Registry (defined
      in Section 6.1), DMARC, the Mail Receiver MUST query the DNS for
      a DMARC TXT record at the DNS domain matching the longest PSD
      (Section 2.3) in place of the RFC5322.From domain in the message
      (if different).  A possibly empty set of records is returned.

   As an example, for a message with the Organizational Domain of
   "", the query for PSD DMARC
   would use "" as the longest PSD
   (Section 2.3).  The receiver would check to see if that PSD is listed
   in the DMARC PSD Registry, and if so, perform the policy lookup at

   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 [RFC7489] policy.  Specifically,
   this is not a mechanism to provide feedback addresses (RUA/RUF) when
   an Organizational Domain has declined to do so.

3.5.  Section 7.  DMARC Feedback

   Operational note for PSD DMARC: For PSOs, feedback for non-existent
   domains is desired and useful.  Because of the constraints on PSD
   DMARC scope, there are no significant privacy considerations
   associated with this reporting (See  See Section 4). 4 for discussion of
   Privacy Considerations.

4.  Privacy Considerations

   This document does not significantly change

   These privacy considerations are developed based on the requiremetns
   of [RFC6973].  The Privacy Considerations of [RFC7489]. [RFC7489] apply to this

4.1.  Feedback leakage

   Providing feedback reporting to PSOs can, in some cases, create
   leakage of information outside of an organization to the PSO.  This
   leakage could be potentially be utilized as part of a program of
   pervasive surveillance (See [RFC7624]).  There are roughly three
   cases to consider:

   o  Branded  Single Organization PSDs (e.g., ".google"), RUA and RUF reports
      based on PSD DMARC have the potential to contain information about
      emails related to entities managed by the organization.  Since
      both the PSO and the Organizational Domain owners are common,
      there is no additional privacy risk for either normal or non-existent non-
      existent Domain reporting. reporting due to PSD DMARC.

   o  Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
      PSD DMARC based reports will only be generated for domains that do
      not publish a DMARC policy at the organizational or host level.
      For domains that do publish the required DMARC policy records, the
      feedback reporting addresses (RUA and RUF) of the organization (or
      hosts) will be used.  Since PSD DMARC is limited to  The only direct feedback leakage risk for
      these PSDs that
      mandate Organizational Domains publish DMARC policy are for existing
      domains, the risk of this issue is limited to Organizational Domains that are out of
      compliance with PSD policy.  Data on non-existent cousin domains
      would be sent to the PSO.

   o  Multi-organization PSDs (e.g., ".com") that do not mandate DMARC
      usage.  Privacy risks for Organizational Domains that have not
      deployed DMARC within such PSDs
      would be are significant.  This is mitigated by the limitation  For non-DMARC
      Organizational Domains, all DMARC feedback will be directed to only
      include PSDs listed in the public IANA DMARC
      PSO.  PSD Registry
      described in Section 6.1. DMARC is opt-out (by publishing a DMARC record at the
      Organizational Domain level) vice opt-in, which would be the more
      desirable characteristic.

   PSOs will receive feedback on non-existent domains, which may be
   similar to existing Organizational Domains.  Feedback related to such
   cousin domains have a small risk of carrying information related to
   an actual Organizational Domain.  To minimize this potential concern,
   PSD DMARC feedback is best limited to Aggregate Reports.  Feedback
   Reports carry more detailed information and present a greater risk.

   Due to the inherent Privacy and Security risks associated with PSD
   DMARC for Organizational Domains in multi-organization PSDs that do
   not particpate in DMARC, any Feedback Reporting related to multi-
   organizational PSDs ought to be limited to non-existent domains
   except in cases where the reporter knows that PSO requires use of

5.  Security Considerations

   This document does not change the Security Considerations of

6.  IANA Considerations

   This section describes actions requested to be completed by IANA.

6.1.  DMARC Public Suffix Domain (PSD) Registry

   IANA is requested to create a new DMARC Public Suffix Domain (PSD)
   Registry within the Domain-based Message Authentication, Reporting,
   [RFC7489] and Conformance (DMARC) Parameters Registry.

   Names [RFC7960].

   The risks of PSDs participating in PSD DMARC must be registered with IANA the issues identified in this new sub-registry.  New entries [RFC7489], Section 12.5,
   External Reporting Addresses, are assigned only for PSDs
   that require use of amplified by PSD DMARC.  The requirement has to be documented in a
   manner that satisfies the terms of Expert Review, per [RFC5226].  The
   Designated Expert needs to confirm that provided documentation
   adequately describes  By design,
   PSD policy to require domain owners to use DMARC
   or that all domain owners are part causes unrequested reporting of a single organization with feedback to entities
   external to the

   The initial set of entries in this registry Organizational Domain.  This is as follows:

   |    PSD      | Reference      | Status        |
   | .bank       | this document  | current       |
   | .insurance  | this document  | current       |
   |     | this discussed in more
   detail in Section 4.

6.  IANA Considerations

   This document  | current       |
   +-------------+----------------+---------------+ does not require any IANA actions.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC7489]  Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
              Message Authentication, Reporting, and Conformance
              (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

7.2.  Informative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,

   [RFC5598]  Crocker, D., "Internet Mail Architecture", RFC 5598,
              DOI 10.17487/RFC5598, July 2009,

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC7624]  Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", RFC 7624,
              DOI 10.17487/RFC7624, August 2015,

   [RFC7960]  Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
              E., Ed., and K. Andersen, Ed., "Interoperability Issues
              between Domain-based Message Authentication, Reporting,
              and Conformance (DMARC) and Indirect Email Flows",
              RFC 7960, DOI 10.17487/RFC7960, September 2016,

   [RFC8020]  Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
              Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
              November 2016, <>.



Author's Address
   Scott Kitterman
   fTLD Registry Services
   600 13th Street, NW, Suite 400
   Washington, DC  20005
   United States of America

   Phone: +1 301 325-5475