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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" docName="draft-ietf-dmarc-psd-14" number="9091" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" category="exp"
     docName="draft-ietf-dmarc-psd-15"
     ipr="trust200902"> consensus="true" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3">

  <front>
    <title abbrev="PSD DMARC">Experimental DMARC Domain-Based Message
    Authentication, Reporting, and Conformance (DMARC) Extension For for Public
    Suffix Domains
    </title>
    <seriesInfo name="RFC" value="9091"/>
    <author initials="S." surname="Kitterman" fullname="Scott Kitterman">
      <organization>fTLD Registry Services</organization>
      <address>
        <postal>
	    <extaddr>Suite 400</extaddr>
	      <street>600 13th Street, NW, Suite 400</street> NW</street>
          <city>Washington</city>
          <region>DC</region>
          <code>20005</code>
          <country>United States of America</country>
        </postal>
        <phone>+1 301 325-5475</phone>
        <email>scott@kitterman.com</email>
      </address>
    </author>
    <author role="editor" initials="T." surname="Wicinski" fullname="Tim Wicinski">
    <organization></organization>
      <organization/>
      <address>
        <postal>
    <street></street>
          <street/>
          <city>Elkins</city>
          <code>26241</code>
    <country>USA</country>
          <country>United States of America</country>
          <region>WV</region>
        </postal>
    <phone></phone>
        <phone/>
        <email>tjw.ietf@gmail.com</email>
    <uri></uri>
        <uri/>
      </address>
    </author>
    <date month="June" year="2021" /> month="July" year="2021"/>
    <keyword>DMARC</keyword>
    <keyword>email authentication</keyword>
    <keyword>TLD</keyword>
    <abstract>
      <t>Domain-based Message Authentication, Reporting, and Conformance
         (DMARC)
         (DMARC), defined in RFC 7489, permits a domain-controlling organization to express
         domain-level policies and preferences for message validation,
         disposition, and reporting, which a mail-receiving organization
         can use to improve mail handling.</t>
      <t>DMARC distinguishes the portion of a name that is a
         Public Suffix Domain (PSD), below which
         organizational domain
         Organizational Domain names are created.  The basic DMARC
         capability allows organizational domains Organizational Domains to specify policies
         that apply to their subdomains, but it does not give that
         capability to PSDs. This document describes an extension to
         DMARC to fully enable DMARC functionality for PSDs.</t>
      <t>Some implementations of DMARC consider a PSD to be ineligible for
         DMARC enforcement.  This specification addresses that case.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="intro" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>DMARC <xref target="RFC7489"/> target="RFC7489" format="default"/> provides a mechanism for publishing
        organizational policy information to email receivers.  DMARC allows policy to be
        specified for both individual domains and for organizational domains Organizational Domains
        and their sub-domains subdomains within a single organization.</t>
      <t>To determine the organizational domain Organizational Domain for a message under
      evaluation, and thus where to look for a policy statement, DMARC makes
      use of a public suffix list. The process for doing this can be found in Section 3.2 of the
      <xref target="RFC7489" sectionFormat="of" section="3.2">the DMARC
        specification.
      specification</xref>.  Currently, the most common public suffix list being used is the
        most common
      one that is maintained by the Mozilla Foundation and made public at <eref target="http://publicsuffix.org">http://publicsuffix.org</eref>.</t> brackets="angle"
      target="https://publicsuffix.org"/>.</t>
      <t>In the basic DMARC model, Public Suffix Domains (PSDs) are not organizational domains Organizational Domains
        and are thus not subject to DMARC processing.  In DMARC, domains
        fall into one of three categories: organizational domains,
        sub-domains Organizational Domains,
        subdomains of organizational domains, Organizational Domains, or PSDs.  A PSD can only
        publish DMARC policy for itself, itself and not for any sub-domains subdomains
        under it.  In some cases, this limitation allows for the abuse
        of non-existent organizational-level domains and hampers
        identification of domain abuse in email.</t>
      <t>This document specifies experimental updates to the DMARC
        specification cited above, <xref target="RFC7489" format="default"/> in an attempt to mitigate this abuse.</t>
      <section anchor="example" title="Example"> numbered="true" toc="default">
        <name>Example</name>

        <t>As an example, imagine a Top-Level Domain (TLD), ".example", that has
        public subdomains for government and commercial use (".gov.example"
        and ".com.example").  The maintainer of a list of such a PSD structure
        would include entries for both of these sub-domains, subdomains, thereby
        indicating that they are PSDs, below which organizational domains Organizational Domains can
        be registered.  Suppose further that there exists a legitimate domain
        called "tax.gov.example", registered within ".gov.example".</t>
     <t>However, by
        <t>By exploiting the typically unauthenticated nature of email, there are
        regular malicious campaigns to impersonate this organization that use
        similar-looking ("cousin") domains such as "t4x.gov.example".  Such
        domains are not registered.</t>
        <t>Within the ".gov.example" public suffix, use of DMARC has been mandated,
        so "gov.example" publishes the following DMARC DNS record:
         <figure><artwork>
        </t>
        <sourcecode><![CDATA[
_dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject;"
                             "rua=mailto:dmc@dmarc.svc.gov.example" )
        </artwork></figure>
        ]]></sourcecode>
        <t>
       This DMARC record provides policy and a reporting destination for
       mail sent from @gov.example.  Similarly, "tax.gov.example" will have
       a DMARC record that specifies policy for mail sent from addresses
       @tax.gov.example.  However, due to DMARC's current method of
       discovering and applying policy at the organizational domain Organizational Domain
       level, the non-existent organizational domain Organizational Domain of @t4x.gov.example
       does not and cannot fall under a DMARC policy.

        </t>
        <t> Defensively registering all variants of "tax" is not a scalable
         strategy.  The intent of this specification, therefore, is to enhance the
         DMARC discovery method by enabling an agent receiving such a
         message to be able to determine that a relevant policy is present at
         "gov.example", which is precluded by the current DMARC specification.
        </t>
      </section>
      <section anchor="discussion" title="Discussion"> numbered="true" toc="default">
        <name>Discussion</name>
        <t> This document provides a simple extension to <xref target="RFC7489"/> target="RFC7489" format="default"/>
         to allow operators of Public Suffix Domains (PSDs) to:
      <list style="symbols">
        <t>Express
        </t>

        <ul spacing="normal">
          <li>Express policy at the level of the PSD that covers all
          organizational domains
          Organizational Domains that do not explicitly publish DMARC records</t>
        <t>Extends records</li>
          <li>Extend the DMARC policy query functionality to detect
            and process such a policy</t>
       <t>Describes policy</li>
          <li>Describe receiver feedback for such policies</t>
       <t>Provides policies</li>
          <li>Provide controls to mitigate potential privacy considerations
       associated with this extension</t>
     </list>
     </t> extension</li>
        </ul>
        <t>This document also provides a new DMARC tag
	to indicate requested handling policy for non-existent subdomains.
	This is provided specifically to support phased deployment of PSD
	DMARC,
	DMARC but is expected to be useful more generally.  Undesired
	rejection risks for mail purporting to be from domains that do not
	exist are substantially lower than for those that do, so the
	operational risk of requesting harsh policy treatment (e.g., reject) is
	lower.
        </t>
        <t>As an additional benefit, the PSD DMARC extension clarifies
        existing requirements.  Based on the requirements of <xref
        target="RFC7489"/>,
        target="RFC7489" format="default"/>, DMARC should function above the
        organizational level for exact domain matches (i.e., if a DMARC record
        were published for "example", then mail from example@example should be
        subject to DMARC processing).  Testing had has revealed that this is not
        consistently applied in different implementations.
        </t>
        <t>There are two types of Public Suffix Operators (PSOs) for which this
         extension would be useful and appropriate:
        </t>
         <t><list style="symbols">
                  <t>Branded

<dl newline="true">

<dt>Branded PSDs (e.g., ".google"): These
</dt>

<dd>These domains are effectively Organizational Domains as discussed in <xref
                      target="RFC7489"/>.
target="RFC7489" format="default"/>. They control all subdomains of the
tree. These are effectively private
                      domains, domains but listed in the current public
suffix list. They are treated as Public public for DMARC purposes. They require the
same protections as DMARC Organizational Domains, Domains but are currently unable to
benefit from DMARC.
                  </t>
                  <t>Multi-organization
</dd>

<dt>Multi-organization PSDs that require DMARC usage (e.g., ".bank"):  Because
</dt>
<dd>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 to extend
to the entire PSD, including cousin domains of registered organizations.
                  </t>
          </list></t>
</dd>

</dl>

        <t>Due to the design of DMARC and the nature of the Internet <xref target="RFC5598">email
        target="RFC5598" format="default">email architecture</xref>, there are
        interoperability issues associated with DMARC deployment.  These are
        discussed in <xref target="RFC7960">
         Interoperability "Interoperability Issues between DMARC Domain-based Message
        Authentication, Reporting, and Conformance (DMARC) and Indirect Email Flows</xref>.
        Flows" <xref target="RFC7960" format="default"/>.  These issues are
        not typically applicable to PSDs, PSDs since they (e.g., the ".gov.example"
        used above) do not typically send mail.
        </t>
      </section>
    </section>
    <section title="Terminology numbered="true" toc="default">
      <name>Terminology and Definitions"> Definitions</name>

      <t>This section defines terms used in the rest of the document.
      </t>
      <section title="Conventions numbered="true" toc="default">
        <name>Conventions Used in This Document">
           <t>The Document</name>

        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
               NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
               "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are
    to be interpreted as described in BCP&nbsp;14 <xref target="RFC2119"/>
    <xref target="RFC8174"/> when, and only when, they appear in all capitals,
    as shown here.
        </t>

      </section>
      <section title="Public numbered="true" toc="default">
        <name>Public Suffix Domain (PSD)"> (PSD)</name>
        <t> The global Internet Domain Name System (DNS) is documented in
               numerous RFCs.  It defines a tree of names
               starting with root, ".", immediately below which are Top Level Top-Level
               Domain names such as ".com" and ".us".

               The domain name structure consists of a tree of names, each of
               which is made of a sequence of words ("labels") separated by
               period characters.  The root of the tree is simply called ".".
               The Internet community at large, through processes and policies
               external to this work, selects points in this tree at which to
               register domain names "owned" by independent organizations.
               Real-world examples are ".com", ".org", ".us", and ".gov.uk".
               Names at which such registrations occur are called Public "Public
               Suffix Domains (PSDs), (PSDs)", and a registration consists of a label
               selected by the registrant to which a desirable PSD is
               appended.  For example, "ietf.org" is a registered domain name,
               and ".org" is its PSD.
        </t>
      </section>
      <section title="Organizational Domain"> numbered="true" toc="default">
        <name>Organizational Domain</name>
        <t> The term Organizational Domains "Organizational Domain" is defined in <xref
                target="RFC7489"/> Section 3.2.</t> target="RFC7489" sectionFormat="of" section="3.2"  format="default"/>.</t>
      </section>
      <section anchor="lpsd" title="Longest PSD"> numbered="true" toc="default">
        <name>Longest PSD</name>
        <t> The longest PSD is the Organizational Domain with one label
               removed. It names the immediate parent node of the Organizational
               Domain in the DNS namespace tree.</t>
      </section>
      <section title="Public numbered="true" toc="default">
        <name>Public Suffix Operator (PSO)"> (PSO)</name>
        <t>A Public Suffix Operator is an organization which that manages
              operations within a PSD, particularly the DNS records published
              for names at and under that domain name.
        </t>
      </section>

      <section title="PSO Controlled numbered="true" toc="default">
        <name>PSO-Controlled Domain Names">
           <t>PSO Controlled Names</name>
        <t>PSO-Controlled Domain Names are names in the DNS that are
               managed by a PSO and are not available for use as Organizational
               Domains.  PSO Controlled  PSO-Controlled Domain Names may have one (e.g., ".com")
               or more (e.g., ".co.uk") name components, depending on PSD policy.
        </t>
      </section>

      <section title="Non-existent Domains"> numbered="true" toc="default">
        <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"/>. target="RFC8020"
        format="default"/>.
        </t>
      </section>
    </section>
    <section title="PSD numbered="true" toc="default">
      <name>PSD DMARC Updates to DMARC Requirements"> Requirements</name>

      <t>To participate in this experiment, implementations should interpret RFC7489
      <xref target="RFC7489"/> as follows:</t> described in the following subsections.</t>
      <section title="General Updates"> numbered="true" toc="default">
        <name>General Updates</name>
        <t>References to "Domain Owners" also apply to PSOs.</t>
      </section>
      <section anchor="genrecfmt" title='Changes numbered="true" toc="default">
        <name>Changes in Section 6.3 "General ("General Record Format"'>
	 <t>If this experiment is successful, this Format")</name>
	<t>The following paragraph is added to this section.  A new tag is
        added after "fo":</t>
	 <t><list style="hanging">
	    <t hangText="np:">
<blockquote>
        <dl newline="false" spacing="normal">
          <dt>np:</dt>
          <dd> Requested Mail Receiver policy for non-existent subdomains
          (plain-text; OPTIONAL). <bcp14>OPTIONAL</bcp14>).  Indicates the policy to be
          enacted by the Receiver at the request of the Domain Owner.  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 "p" tag defined below.  If the "np" tag
          is absent, the policy specified by the "sp" tag (if the "sp" tag is
          present) or the policy specified by the "p" tag,
	     if tag (if the "sp" tag is not present, MUST
          absent) <bcp14>MUST</bcp14> be applied for non-existent subdomains.
          Note that "np" 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
	     DMARC Section 6.6.3.
	    </t>
         </list></t> <xref
          target="RFC7489" sectionFormat="of" section="6.6.3"></xref>.
	  </dd>

        </dl>
</blockquote>

        <t>The following tag definitions from DMARC are updated:
        </t>
	 <t><list style="hanging">
	    <t hangText="p:">The

        <dl newline="false" spacing="normal">
          <dt>p:</dt>
          <dd>The sentence 'Policy applies to the domain queried and to
          subdomains, unless subdomain policy is explicitly described using
          the "sp" tag' is updated to read 'Policy applies to the domain
          queried and to subdomains, unless subdomain policy is explicitly
          described using the "sp" or "np" tags.'
	    </t>
	    <t hangText="sp:">The
	  </dd>
          <dt>sp:</dt>
          <dd>The sentence 'If absent, the policy specified by the "p" tag MUST
          <bcp14>MUST</bcp14> be applied for subdomains' is updated to read
          'If both the "sp" tag is absent and the "np" tag is either absent or
          not applicable, the policy specified by the "p" tag MUST
          <bcp14>MUST</bcp14> be applied for subdomains.
	    </t>
         </list></t> subdomains.'
	  </dd>
        </dl>

      </section>
     <section title='Changes

<section>
<name>Changes in Section 6.4 "Formal Definition"'> ("Formal Definition")</name>
      <t>The ABNF <xref target="RFC5234"/> for DMARC shall is updated to include a new definition
        "dmarc-nprequest" which is defined as:
          <figure><artwork> definition,
      "dmarc-nprequest": </t>
         <sourcecode type="abnf"><![CDATA[
            dmarc-nprequest =  "np" *WSP "=" *WSP
                ( "none" / "quarantine" / "reject" )

          </artwork></figure>
]]></sourcecode>
<t>          The "dmarc-record" definition is also updated to include the following:
          <figure><artwork> following:</t>
<sourcecode><![CDATA[
dmarc-record    = dmarc-version dmarc-sep
              [dmarc-request]
              [dmarc-sep dmarc-srequest]
              [dmarc-sep dmarc-auri]
              [dmarc-sep dmarc-furi]
              [dmarc-sep dmarc-adkim]
              [dmarc-sep dmarc-aspf]
              [dmarc-sep dmarc-ainterval]
              [dmarc-sep dmarc-fo]
              [dmarc-sep dmarc-rfmt]
              [dmarc-sep dmarc-percent]
              [dmarc-sep]
              [dmarc-sep dmarc-nprequest]
          </artwork></figure>
      </t>
              ; components other than dmarc-version and
              ; dmarc-request may appear in any order
]]></sourcecode>

</section>
      <section title='Changes numbered="true" toc="default">
        <name>Changes in Section 6.5 "Domain ("Domain Owner Actions"'> Actions")</name>
        <t>In addition to the DMARC domain owner Domain Owner actions, PSOs that require
        use of DMARC and participate in PSD DMARC ought to make that
        information available to receivers. This document is an experimental
        mechanism for doing so.  See so; see the [this document] description in <xref
             target="experiment">experiment description</xref>.
        target="registry" format="default"/>.
        </t>
      </section>
      <section title='Changes numbered="true" toc="default">
        <name>Changes in Section 6.6.1 "Extract ("Extract Author Domain"'> Domain")</name>
        <t> Experience with DMARC has shown that some implementations
        short-circuit messages, bypassing DMARC policy application, when the
        domain name extracted by the receiver (from the RFC5322.From) RFC5322.From domain) is on
        the public suffix list used by the receiver.  This negates the
        capability being created by this specification.  Therefore, the
        following paragraph is appended to Section 6.6.1
             of DMARC: <xref target="RFC7489"
        sectionFormat="of" section="6.6.1">the DMARC
        specification</xref>:
        </t>
         <t>
<blockquote>
        Note that domain names that appear on a public suffix list are
             not exempt from DMARC policy application and reporting.
         </t>
</blockquote>
      </section>
      <section anchor="poldis" title='Changes numbered="true" toc="default">
        <name>Changes in Section 6.6.3 "Policy Discovery"'> ("Policy Discovery")</name>
        <t>A new step is added between step steps 3 and 4 is added:</t>
         <t><list style="hanging">
               <t hangText="3A.">If 4:</t>

<blockquote>
        <dl newline="false" spacing="normal">

          <dt>3A.</dt>
          <dd>If the set is now empty and the longest PSD ([RFC9091], <xref
                   target="lpsd">longest PSD</xref> target="lpsd"
          format="default"></xref>) of the Organizational Domain is
          one that the receiver has determined is acceptable for PSD DMARC (discussed
          (based on the data in one of the [this document] DMARC PSD Registry Examples described
          in <xref
                   target="experiment">experiment description</xref>), target="registry" format="default"></xref> of [RFC9091]), the
          Mail Receiver MUST <bcp14>MUST</bcp14> query the DNS for a DMARC TXT record
	    at the DNS domain matching the [this document] <xref target="lpsd"> longest PSD</xref> PSD in place of the RFC5322.From
          domain in the message (if different).  A possibly empty set of
          records is returned.
               </t>
         </list> </t>
          </dd>
        </dl>
</blockquote>
        <t>As an example, for a message with the Organizational Domain of
        "example.compute.cloudcompany.com.example", the query for PSD DMARC
        would use "compute.cloudcompany.com.example" as the [this document]
             <xref
             target="lpsd">longest PSD</xref>.
        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
        "_dmarc.compute.cloudcompany.com.example".
        </t>
         <t>Note:

        <t indent="3">Note: Because the PSD policy query comes after the Organizational
        Domain policy query, PSD policy is not used for Organizational
             domains 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 title='Changes numbered="true" toc="default">
        <name>Changes in Section 7 "DMARC Feedback"'>
         <t>If this experiment is successful, this ("DMARC Feedback")</name>
        <t>The following paragraph is added to this section.</t> section:</t>
<blockquote>
        <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 <xref target="privacy"/> target="privacy"
        format="default"/> of [this document] [RFC9091] for discussion of Privacy Considerations privacy
        considerations for PSD DMARC.
        </t>
</blockquote>
      </section>
    </section>

    <section anchor="privacy" title="Privacy Considerations"> numbered="true" toc="default">
      <name>Privacy Considerations</name>
      <t>These privacy considerations are developed based on the requirements of
          <xref target="RFC6973"/>. target="RFC6973" format="default"/>.
          Additionally, the Privacy Considerations privacy considerations of <xref target="RFC7489"/> target="RFC7489" format="default"/>
          apply to the mechanisms described by this document.
          To participate in this experiment, implementations should be aware of
          the privacy considerations described in this section.  If this
	    experiment is successful, this section should be incorporated into the Privacy Considerations
          "Privacy Considerations" section as "Feedback leakage". Leakage".
      </t>
      <t>Providing feedback reporting to PSOs can, in some cases, cause
           information to leak out of an organization to the PSO.
	         This leakage could potentially be utilized as part of a program
		       of pervasive surveillance (See (see <xref target="RFC7624"/>). target="RFC7624" format="default"/>).  There
		             are roughly three cases to consider:
      </t>
          <t><list style="symbols">
                  <t>Single
<dl newline="true">

<dt>Single Organization PSDs (e.g., ".google"), RUA ".google"):
</dt>
<dd>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 Owners are common, there is
no additional privacy risk for either normal or non-existent
		      Domain domain reporting
due to PSD DMARC.
                  </t>
                  <t>Multi-organization
</dd>

<dt>Multi-organization PSDs that require DMARC usage (e.g., ".bank"):
</dt>
<dd>Reports based on 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.  The only direct
risk of feedback leakage risk for these PSDs are for Organizational Domains that are
out of compliance with PSD policy.  Data on non-existent cousin domains would
be sent to the PSO.
                  </t>
                  <t>Multi-organization
</dd>

<dt>Multi-organization PSDs (e.g., ".com") that do not mandate DMARC usage:  Privacy
</dt>
<dd>Privacy risks for Organizational Domains that have not deployed DMARC
within such PSDs are significant.  For non-DMARC Organizational Domains, all
DMARC feedback will be directed to the PSO.  PSD DMARC is
		      opt-out opt out (by
publishing a DMARC record at the Organizational Domain level) instead of opt-in,
opt in, which would be the more desirable characteristic.  This means that any
non-DMARC organizational domain Organizational Domain would have its feedback
		      reports Feedback Reports redirected to
the PSO.  The content of such reports, particularly for existing domains, is
privacy sensitive.
                  </t>
          </list></t>
</dd>

</dl>

  <t>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 MUST <bcp14>MUST</bcp14> be limited to Aggregate Reports. Feedback
  Reports carry more detailed information and present a greater risk.
  </t>
      <t>Due to the inherent Privacy privacy and Security security risks associated with
            PSD DMARC for Organizational Domains in multi-organization PSDs
        that do not participate in DMARC, any Feedback Reporting feedback reporting
        related to multi-organizational PSDs MUST <bcp14>MUST</bcp14> be limited
        to non-existent domains
        except in cases where the reporter knows that PSO
	      requires use of DMARC (by checking the DMARC PSD Registry).
      </t>
    </section>
    <section title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t> This document does not change the Security Considerations security considerations of
          <xref target="RFC7489"/> target="RFC7489" format="default"/> and <xref target="RFC7960"/>. target="RFC7960" format="default"/>.
      </t>
      <t> The risks of the issues identified in <xref target="RFC7489"/>,
	  Section 12.3, DNS Security, target="RFC7489"
      sectionFormat="of" section="12.3" format="default"/> ("DNS Security") are
      amplified by PSD DMARC.  In particular, consequences of DNS cache poisoning (or Name Chaining), see <xref
	  target="RFC3833"/> for details, consequences name
      chaining) are increased because a successful attack would potentially
      have a much wider scope. scope (see <xref target="RFC3833" format="default"/>
      for details).
      </t>
      <t> The risks of the issues identified in <xref target="RFC7489"/>,
	  Section 12.5, External target="RFC7489"
      sectionFormat="of" section="12.5" format="default"/> ("External Reporting Addresses,
      Addresses") are amplified by PSD DMARC.  By design, PSD DMARC causes
      unrequested reporting of feedback to entities external to the
      Organizational Domain.  This is discussed in more detail in <xref target="privacy"/>.
      target="privacy" format="default"/>.
      </t>
    </section>
    <section anchor="iana" title="IANA Considerations">
       <t>This section describes actions requested to be completed by IANA.</t>

       <section anchor="iana1" title="Subdomain Policy Tag"> numbered="true" toc="default">
      <name>IANA Considerations</name>

        <t>IANA is requested to add has added a new tag to DMARC the "DMARC Tag Registry Registry" in the Domain-based
        "Domain-based Message Authentication, Reporting, and Conformance
        (DMARC) Parameters Registry. Parameters" registry. The "Status" column is defined in <xref target="RFC7489"/>Section 11.4.
        target="RFC7489" sectionFormat="of" section="11.4" format="default"/>.
        </t>
        <t>The new entry is as follows:
            <figure><artwork>
+----------+-----------+---------+-------------------------------+
| Tag Name | Reference | Status  | Description                   |
+----------+-----------+---------+-------------------------------+
| np       | this      | current | Requested
        </t>

<table anchor="table_1">
  <name></name>
  <thead>
    <tr>
      <th>Tag Name</th>
      <th>Reference</th>
      <th>Status</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>np</td>
      <td>RFC 9091</td>
      <td>current</td>
      <td>Requested handling policy for |
|          | document  |         | non-existent subdomains       |
+----------+-----------+---------+-------------------------------+
            </artwork> </figure>
  [RFC EDITOR: Please replace "This document" with the RFC number of this document.] subdomains</td>
    </tr>

  </tbody>
</table>

    <t>

    </t>
    </section>
   </section>
  </middle>
  <back>
   <references title="Normative References">
      <?rfc include="reference.RFC.2119" ?>
      <?rfc include="reference.RFC.7489" ?>
      <?rfc include="reference.RFC.8174" ?>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <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.7489.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.5234.xml"/>
      </references>

   <references title="Informative References">
      <?rfc include="reference.RFC.3833" ?>
      <?rfc include="reference.RFC.8126" ?>
      <?rfc include="reference.RFC.5598" ?>
      <?rfc include="reference.RFC.6973" ?>
      <?rfc include="reference.RFC.7624" ?>
      <?rfc include="reference.RFC.7960" ?>
      <?rfc include="reference.RFC.8020" ?>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3833.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.5598.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6973.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7624.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7960.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8020.xml"/>

        <reference anchor="psddmarc.org" anchor="PSD-DMARC" target="https://psddmarc.org/">
          <front>
            <title>PSD DMARC Web Site</title>
            <title>Public Suffix Domain DMARC</title>
            <author>
               <organization>multiple</organization>
            </author>
            <date month="April" year="2019" />
          </front>
        </reference>
      </references>
    </references>
    <section anchor="experiment"
    title="PSD numbered="true" toc="default">
      <name>PSD DMARC Privacy Concern Mitigation Experiment"> Experiment</name>
      <t>The experiment being performed has three different questions which that are
      looking to be addressed in this document. </t>
    <t><list style="symbols">

    <t>Section 3.2
      <ul spacing="normal">
        <li><xref target="genrecfmt"/> modifies policy discovery to add an
        additional DNS lookup.  To determine if this lookup is useful, PSDs
        will add additional DMARC records in place, place and will analyze the DMARC
        reports.  Success will be determined if a consensus of PSDs that
        publish DMARC records are able to collect useful data.</t>
    <t>Section 3.2 data.</li>
        <li><xref target="genrecfmt"/> adds the "np" tag for non-existent
        subdomains (DNS NXDOMAIN).  PSOs wishing to test this will add this
        flag to their DMARC record, record and will analyze DMARC reports for
        deployment.  Success will be determined if organizations find
        explicitly blocking non-existent subdomains domains desirable and provide that doing
        so provides added value. </t>
    <t> Section 4.1 </li>
        <li><xref target="privacy"/> discusses three cases where providing
        feedback could cause information to leak out of an organization.  This
        experiment will analyze the feedback reports Feedback Reports generated for each case
        to determine if there is information leakage.</t>
</list></t> leakage.</li>
      </ul>

    </section>
    <section anchor="registry" title="DMARC numbered="true" toc="default">
      <name>DMARC PSD Registry Examples">
	   <t> To Examples</name>
      <t>To facilitate experimentation around mitigation of data leakage mitigation, leakage, samples
      of the DNS based DNS-based and IANA like IANA-like registries are available at <xref target="psddmarc.org"/>.
      target="PSD-DMARC" format="default"/>.
      </t>
      <section anchor="dnsregistry" title="DMARC numbered="true" toc="default">
        <name>DMARC PSD DNS Query Service"> Service</name>
        <t> A sample stand-alone DNS query service is available at <xref
	       target="psddmarc.org"/>.
        target="PSD-DMARC" format="default"/>.  It was developed based on the
        contents suggested for an IANA registry in an earlier revision draft version of this draft.
        document.  Usage of the service is described on the web site. at <xref
        target="PSD-DMARC" format="default"/>.
        </t>
      </section>

      <section anchor="iana2" title="DMARC Public Suffix Domain (PSD) Registry"> numbered="true" toc="default">
        <name>DMARC PSD Registry</name>
        <t> <xref target="psddmarc.org"/> target="PSD-DMARC" format="default"/> provides an IANA like IANA-like
        DMARC Public Suffix Domain (PSD) Registry as a stand-alone DNS query
        service.  It follows the contents and structure described below.
        There is a Comma
	       Separated Comma-Separated Value (CSV) version of the listed PSD domains which PSDs
        that is suitable for use in build updates for PSD DMARC capable DMARC-capable software.
        </t>
        <t>PSDs that are deploying DMARC and are participating in PSD DMARC
            must register their public suffix domain in this
	           new registry.   The requirement has to be documented in a
		          manner that satisfies the terms of Expert Review, per <xref
	       target="RFC8126"/>. target="RFC8126" format="default"/>.  The Designated Expert needs to confirm that
			         provided documentation adequately describes PSD policy to require
	       domain owners
				        Domain Owners to use DMARC or that all domain owners Domain Owners are part of
					       a single organization with the PSO.
        </t>
        <t>The initial set of entries in this authoritative registry is as follows:
            <figure><artwork>
+-------------+---------------+
|    PSD      | Status        |
+-------------+---------------+
| .bank       | current       |
+-------------+---------------+
| .insurance  | current       |
+-------------+---------------+
| .gov.uk     | current       |
+-------------+---------------+
| .mil        | current       |
+-------------+---------------+
            </artwork> </figure>
           </t> can be found here:
          <eref brackets="angle" target="https://psddmarc.org"/></t>

      </section>
      <section anchor="pslplus" title="DMARC numbered="true" toc="default">
        <name>DMARC PSD PSL Extension"> Extension</name>
        <t> <xref target="psddmarc.org"/> target="PSD-DMARC" format="default"/> provides a file formatted like the
               Public Suffix List (PSL) in order to
               facilitate identification of PSD DMARC participants.  Contents are
               functionally identical to the IANA like registry, IANA-like registry but presented in
               a different format.
        </t>
        <t> When using this approach, the input domain of the extension lookup
               is supposed to be the output domain of the regular PSL lookup, i.e.,
               the organizational domain. Organizational Domain.  This alternative data approach is
               potentially useful since DMARC implementations already need to be
               able to parse the data format, so it should be easier to implement.
        </t>
      </section>
    </section>
    <section anchor="implementations" title="Implementations"> numbered="true" toc="default">
      <name>Implementations</name>
      <t> There are two known implementations of PSD DMARC available for testing.
      </t>
      <section title="Authheaders Module"> numbered="true" toc="default">
        <name>Authheaders Module</name>
        <t>The authheaders Python module and command line tool is available
	    for download or installation from Pypi (Python Packaging Index).
        </t>
        <t>It supports both use of the DNS based DNS-based query service and download
	    of the CSV registry file from <xref target="psddmarc.org"/>. target="PSD-DMARC" format="default"/>.
        </t>
      </section>
      <section title="Zdkimfilter Module"> numbered="true" toc="default">
        <name>Zdkimfilter Module</name>
        <t>The zdkimfilter module is a separately available add-on to
            Courier-MTA.
        </t>
        <t>Mostly used for DKIM DomainKeys Identified Mail (DKIM) signing, it can
        be configured to also verify, apply DMARC policies, and send aggregate reports. Aggregate
        Reports.  For PSD DMARC DMARC, it uses the PSL extension list approach, which
        is available from <xref target="psddmarc.org"/> target="PSD-DMARC" format="default"/>.
        </t>
      </section>
    </section>
    <section anchor="thanks" title="Acknowledgements" numbered="no"> numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t> Thanks to the following individuals for their contributions (both
      public and private) to improving this document.  Special shout out document:
      <contact fullname="Kurt Andersen"/>, <contact fullname="Seth
      Blank"/>, <contact fullname="Dave Crocker"/>, <contact fullname="Heather
      Diaz"/>, <contact fullname="Tim Draegen"/>, <contact fullname="Zeke
      Hendrickson"/>, <contact fullname="Andrew Kennedy"/>, <contact
      fullname="John Levine"/>, <contact fullname="Dr. Ian Levy"/>, <contact
      fullname="Craig Schwartz"/>, <contact fullname="Alessandro Vesely"/>,
      and <contact fullname="Tim Wicinski"/>.</t>
      <t>A special mention to
	  Dave Crocker
      <contact fullname="Dave Crocker"/> for naming coming up with the beast.</t>
      <t> Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen,
	  Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig
	  Schwartz, Alessandro Vesely, and Tim Wicinski</t> name.</t>
    </section>

  </back>
</rfc>