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<pre>Internet Engineering Task Force (IETF) S. Kitterman
Request for Comments: 6652 Agari
Updates: <a href="./rfc4408">4408</a> June 2012
Category: Standards Track
ISSN: 2070-1721
<span class="h1">Sender Policy Framework (SPF) Authentication Failure Reporting</span>
<span class="h1">Using the Abuse Reporting Format</span>
Abstract
This memo presents extensions to the Abuse Reporting Format (ARF) and
Sender Policy Framework (SPF) specifications to allow for detailed
reporting of message authentication failures in an on-demand fashion.
This memo updates <a href="./rfc4408">RFC 4408</a> by providing an IANA registry for SPF
modifiers.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in <a href="./rfc5741#section-2">Section 2 of RFC 5741</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="http://www.rfc-editor.org/info/rfc6652">http://www.rfc-editor.org/info/rfc6652</a>.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
<span class="grey">Kitterman Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-2">2</a>
<a href="#section-2">2</a>. Definitions .....................................................<a href="#page-3">3</a>
<a href="#section-2.1">2.1</a>. Key Words ..................................................<a href="#page-3">3</a>
<a href="#section-2.2">2.2</a>. Imported Definitions .......................................<a href="#page-3">3</a>
<a href="#section-3">3</a>. Optional Reporting Address for SPF ..............................<a href="#page-3">3</a>
<a href="#section-4">4</a>. Requested Reports ...............................................<a href="#page-4">4</a>
<a href="#section-4.1">4.1</a>. Requested Reports for SPF Failures .........................<a href="#page-5">5</a>
<a href="#section-5">5</a>. IANA Considerations .............................................<a href="#page-5">5</a>
<a href="#section-5.1">5.1</a>. SPF Modifier Registration ..................................<a href="#page-5">5</a>
<a href="#section-6">6</a>. Security Considerations .........................................<a href="#page-6">6</a>
<a href="#section-6.1">6.1</a>. Identity Selection .........................................<a href="#page-6">6</a>
<a href="#section-6.2">6.2</a>. Report Volume ..............................................<a href="#page-6">6</a>
<a href="#section-7">7</a>. References ......................................................<a href="#page-7">7</a>
<a href="#section-7.1">7.1</a>. Normative References .......................................<a href="#page-7">7</a>
<a href="#section-7.2">7.2</a>. Informative References .....................................<a href="#page-7">7</a>
<a href="#appendix-A">Appendix A</a>. Acknowledgements .......................................<a href="#page-8">8</a>
<a href="#appendix-B">Appendix B</a>. Examples ...............................................<a href="#page-8">8</a>
B.1. SPF DNS Record for Domain That Sends No Mail but
Requests Reports ...........................................<a href="#page-8">8</a>
B.2. Minimal SPF DNS Record Change to Add a Reporting
Address ....................................................<a href="#page-8">8</a>
B.3. SPF DNS Record with Reporting Address, Report
Percentage, and Requested Report Type ......................<a href="#page-8">8</a>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The Abuse Reporting Format [<a href="#ref-ARF" title=""An Extensible Format for Email Feedback Reports"">ARF</a>] defines a message format for sending
reports of abuse in the messaging infrastructure, with an eye toward
automating both the generation and consumption of those reports.
The Sender Policy Framework [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] is one mechanism for message sender
authentication; it is "path-based", meaning it authenticates the
route that a message took from origin to destination. The output is
a verified domain name that can then be subjected to some sort of
evaluation process (e.g., comparison to a known-good list, submission
to a reputation service, etc.).
This document extends [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] to add an optional reporting address and
other parameters. Extension of [<a href="#ref-ARF" title=""An Extensible Format for Email Feedback Reports"">ARF</a>] to add features required for
the reporting of these incidents is covered in [<a href="#ref-ARF-AUTHFAIL">ARF-AUTHFAIL</a>] and
[<a href="#ref-ARF-AS" title=""Creation and Use of Email Feedback Reports: An Applicability Statement for the Abuse Reporting Format (ARF)"">ARF-AS</a>].
This document additionally creates a an IANA registry of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] record
modifiers to avoid modifier namespace collisions.
<span class="grey">Kitterman Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Definitions</span>
<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>. Key Words</span>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [<a href="#ref-KEYWORDS" title=""Key words for use in RFCs to Indicate Requirement Levels"">KEYWORDS</a>].
<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>. Imported Definitions</span>
The [<a href="#ref-ABNF" title=""Augmented BNF for Syntax Specifications: ABNF"">ABNF</a>] token "qp-section" is defined in [<a href="#ref-MIME" title=""Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"">MIME</a>].
"local-part" is defined in [<a href="#ref-MAIL" title=""Internet Message Format"">MAIL</a>].
"addr-spec" is defined in [<a href="#ref-MAIL" title=""Internet Message Format"">MAIL</a>].
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Optional Reporting Address for SPF</span>
There exist cases in which an ADministrative Management Domain (ADMD)
(see [<a href="#ref-EMAIL-ARCH">EMAIL-ARCH</a>]) employing [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] for announcing sending practices
may want to know when messages are received via unauthorized routing.
Currently, there is no such method defined in conjunction with
standardized approaches such as [<a href="#ref-ARF" title=""An Extensible Format for Email Feedback Reports"">ARF</a>]. Similar information can be
gathered using a specially crafted [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] record and a special DNS
server to track [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] record lookups.
This document defines the following optional "modifier" (as defined
in Section 4.6.1 of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>]) to SPF records, using the form defined in
that specification:
ra= Reporting Address (plain-text; OPTIONAL; no default). MUST be a
local-part (see Section 3.4.1 of [<a href="#ref-MAIL" title=""Internet Message Format"">MAIL</a>]) specifying an e-mail
address to which a report SHOULD be sent when mail claiming to
be from this domain (see Section 2.4 of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] for a description
of how domains are identified for SPF checks) has failed the
evaluation algorithm described in [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>], in particular because a
message arrived via an unauthorized route. To generate a
complete address to which the report is sent, the Verifier
simply appends to this value an "@" followed by the
SPF-compliant domain per Section 4.1 of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>]. ra= modifiers in
a record that was reached by following an "include" mechanism
(defined in Section 5.2 of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>]) MUST be ignored.
ABNF:
spf-report-tag = "ra=" qp-section
<span class="grey">Kitterman Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
rp= Requested Report Percentage (plain-text; OPTIONAL; default is
"100"). The value is an integer from 0 to 100 inclusive that
indicates what percentage of incidents of SPF failures, selected
at random, are to cause reports to be generated. The report
generator SHOULD NOT issue reports for more than the requested
percentage of incidents. An exception to this might be some
out-of-band arrangement between two parties to override it with
some mutually agreed value. Report generators MAY make use of
the "Incidents:" field in [<a href="#ref-ARF" title=""An Extensible Format for Email Feedback Reports"">ARF</a>] to indicate that there are more
reportable incidents than there are reports.
ABNF:
spf-rp-tag = "rp=" 1*12DIGIT "/" 1*12DIGIT
rr= Requested Reports (plain-text; OPTIONAL; default is "all"). The
value MUST be a colon-separated list of tokens representing
those conditions under which a report is desired. See
<a href="#section-4.1">Section 4.1</a> for a list of valid tags.
ABNF:
spf-rr-type = ( "all" / "e" / "f" / "s" / "n" )
spf-rr-tag = "rr=" spf-rr-type *( ":" spf-rr-type )
In the absence of an "ra=" tag in the SPF record, the "rp=" and "rr="
tags MUST be ignored, and the report generator MUST NOT issue a
report.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Requested Reports</span>
This memo also includes, as the "rr" tokens defined above, the means
by which the sender can request reports for specific circumstances of
interest. Verifiers MUST NOT generate reports for incidents that do
not match a requested report and MUST ignore requests for reports not
included in this list.
<span class="grey">Kitterman Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. Requested Reports for SPF Failures</span>
The following report requests are defined for SPF results:
all All reports are requested.
e Reports are requested for messages that produced an SPF result
of "TempError" or "PermError".
f Reports are requested for messages that produced an SPF result
of "Fail".
s Reports are requested for messages that produced an SPF result
of "SoftFail".
n Reports are requested for messages that produced an SPF result
of "Neutral" or "None".
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. IANA Considerations</span>
As required by [<a href="#ref-IANA-CONS">IANA-CONS</a>], this section contains registry
information for the new [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] modifiers.
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. SPF Modifier Registration</span>
IANA has created the Modifier Names registry under Sender Policy
Framework Parameters, to include a list of all registered SPF
modifier names and their defining documents.
New registrations or updates are to be published in accordance with
the "Specification Required" guidelines as described in [<a href="#ref-IANA-CONS">IANA-CONS</a>].
New registrations and updates MUST contain the following information:
1. Name of the modifier being registered or updated
2. The document in which the specification of the modifier is
published
3. New or updated status, which MUST be one of the following:
Current: The field is in current use
Deprecated: The field might be in current use but its use is
discouraged
Historic: The field is no longer in current use
<span class="grey">Kitterman Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
An update may make a notation on an existing registration indicating
that a registered field is historic or deprecated if appropriate.
+------------+-----------------+---------+
| MODIFIER | REFERENCE | STATUS |
+------------+-----------------+---------+
| exp | <a href="./rfc4408">RFC 4408</a> | Current |
| redirect | <a href="./rfc4408">RFC 4408</a> | Current |
| ra | (this document) | Current |
| rp | (this document) | Current |
| rr | (this document) | Current |
+------------+-----------------+---------+
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. Security Considerations</span>
Inherited considerations: implementers are advised to consider the
Security Considerations sections of [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>], [<a href="#ref-ARF" title=""An Extensible Format for Email Feedback Reports"">ARF</a>], [<a href="#ref-ARF-AS" title=""Creation and Use of Email Feedback Reports: An Applicability Statement for the Abuse Reporting Format (ARF)"">ARF-AS</a>], and
[<a href="#ref-ARF-AUTHFAIL">ARF-AUTHFAIL</a>].
In addition to the advice in the Security Considerations section of
[<a href="#ref-ARF-AS" title=""Creation and Use of Email Feedback Reports: An Applicability Statement for the Abuse Reporting Format (ARF)"">ARF-AS</a>], these additional considerations apply to the generation of
[<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] authentication failure reports:
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Identity Selection</span>
Preventing an [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] failure for SPF authentication failure reports is
essential to mitigate the risk of data loops.
If the [<a href="#ref-SMTP" title=""Simple Mail Transfer Protocol"">SMTP</a>] return address to be used will not be the NULL
return address, i.e., "MAIL FROM:<>", then the selected return
address MUST be selected such that it will pass [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] MAIL FROM
checks upon initial receipt.
If the report is passed to the Message Submission Agent (MSA) (MSA
is described in [<a href="#ref-EMAIL-ARCH">EMAIL-ARCH</a>] using [<a href="#ref-SMTP" title=""Simple Mail Transfer Protocol"">SMTP</a>]), the HELO/EHLO command
parameter SHOULD also be selected so that it will pass [<a href="#ref-SPF" title=""Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1"">SPF</a>] HELO
checks.
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Report Volume</span>
It is impossible to predict the volume of reports this facility will
generate when enabled by a report receiver. An implementer ought to
anticipate substantial volume, since the amount of abuse occurring at
receivers cannot be known ahead of time, and may vary rapidly and
unpredictably.
<span class="grey">Kitterman Standards Track [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. References</span>
<span class="h3"><a class="selflink" id="section-7.1" href="#section-7.1">7.1</a>. Normative References</span>
[<a id="ref-ABNF">ABNF</a>] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, <a href="./rfc5234">RFC 5234</a>,
January 2008.
[<a id="ref-ARF">ARF</a>] Shafranovich, Y., Levine, J., and M. Kucherawy, "An
Extensible Format for Email Feedback Reports", <a href="./rfc5965">RFC 5965</a>,
August 2010.
[<a id="ref-ARF-AS">ARF-AS</a>] Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
Feedback Reports: An Applicability Statement for the Abuse
Reporting Format (ARF)", <a href="./rfc6650">RFC 6650</a>, June 2012.
[<a id="ref-ARF-AUTHFAIL">ARF-AUTHFAIL</a>]
Fontana, H., "Authentication Failure Reporting Using the
Abuse Reporting Format", <a href="./rfc6591">RFC 6591</a>, April 2012.
[<a id="ref-IANA-CONS">IANA-CONS</a>]
Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", <a href="https://www.rfc-editor.org/bcp/bcp26">BCP 26</a>, <a href="./rfc5226">RFC 5226</a>,
May 2008.
[<a id="ref-KEYWORDS">KEYWORDS</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-MAIL">MAIL</a>] Resnick, P., Ed., "Internet Message Format", <a href="./rfc5322">RFC 5322</a>,
October 2008.
[<a id="ref-MIME">MIME</a>] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", <a href="./rfc2045">RFC 2045</a>, November 1996.
[<a id="ref-SMTP">SMTP</a>] Klensin, J., "Simple Mail Transfer Protocol", <a href="./rfc5321">RFC 5321</a>,
October 2008.
[<a id="ref-SPF">SPF</a>] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
for Authorizing Use of Domains in E-Mail, Version 1",
<a href="./rfc4408">RFC 4408</a>, April 2006.
<span class="h3"><a class="selflink" id="section-7.2" href="#section-7.2">7.2</a>. Informative References</span>
[<a id="ref-EMAIL-ARCH">EMAIL-ARCH</a>]
Crocker, D., "Internet Mail Architecture", <a href="./rfc5598">RFC 5598</a>,
July 2009.
<span class="grey">Kitterman Standards Track [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc6652">RFC 6652</a> SPF Auth Failure Reporting June 2012</span>
<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Acknowledgements</span>
The author wishes to acknowledge the following for their review and
constructive criticism of this proposal: Murray Kucherawy, Tim
Draegen, Julian Mehnle, and John Levine.
<span class="h2"><a class="selflink" id="appendix-B" href="#appendix-B">Appendix B</a>. Examples</span>
<span class="h3"><a class="selflink" id="appendix-B.1" href="#appendix-B.1">B.1</a>. SPF DNS Record for Domain That Sends No Mail but Requests Reports</span>
v=spf1 ra=postmaster -all
<span class="h3"><a class="selflink" id="appendix-B.2" href="#appendix-B.2">B.2</a>. Minimal SPF DNS Record Change to Add a Reporting Address</span>
v=spf1 mx:example.org ra=postmaster -all
<span class="h3"><a class="selflink" id="appendix-B.3" href="#appendix-B.3">B.3</a>. SPF DNS Record with Reporting Address, Report Percentage, and</span>
Requested Report Type
v=spf1 mx:example.org -all ra=postmaster rp=10 rr=e
Author's Address
Scott Kitterman
Agari
3611 Scheel Dr.
Ellicott City, MD 21042
US
Phone: +1 301 325 5475
EMail: scott@kitterman.com
Kitterman Standards Track [Page 8]
</pre>
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