7Internet Engineering Task Force (IETF) S. Kitterman
8Request for Comments: 6652 Agari
10Category: Standards Track
14 Sender Policy Framework (SPF) Authentication Failure Reporting
15 Using the Abuse Reporting Format
19 This memo presents extensions to the Abuse Reporting Format (ARF) and
20 Sender Policy Framework (SPF) specifications to allow for detailed
21 reporting of message authentication failures in an on-demand fashion.
23 This memo updates RFC 4408 by providing an IANA registry for SPF
28 This is an Internet Standards Track document.
30 This document is a product of the Internet Engineering Task Force
31 (IETF). It represents the consensus of the IETF community. It has
32 received public review and has been approved for publication by the
33 Internet Engineering Steering Group (IESG). Further information on
34 Internet Standards is available in Section 2 of RFC 5741.
36 Information about the current status of this document, any errata,
37 and how to provide feedback on it may be obtained at
38 http://www.rfc-editor.org/info/rfc6652.
42 Copyright (c) 2012 IETF Trust and the persons identified as the
43 document authors. All rights reserved.
45 This document is subject to BCP 78 and the IETF Trust's Legal
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50 to this document. Code Components extracted from this document must
51 include Simplified BSD License text as described in Section 4.e of
52 the Trust Legal Provisions and are provided without warranty as
53 described in the Simplified BSD License.
58Kitterman Standards Track [Page 1]
60RFC 6652 SPF Auth Failure Reporting June 2012
65 1. Introduction ....................................................2
66 2. Definitions .....................................................3
67 2.1. Key Words ..................................................3
68 2.2. Imported Definitions .......................................3
69 3. Optional Reporting Address for SPF ..............................3
70 4. Requested Reports ...............................................4
71 4.1. Requested Reports for SPF Failures .........................5
72 5. IANA Considerations .............................................5
73 5.1. SPF Modifier Registration ..................................5
74 6. Security Considerations .........................................6
75 6.1. Identity Selection .........................................6
76 6.2. Report Volume ..............................................6
77 7. References ......................................................7
78 7.1. Normative References .......................................7
79 7.2. Informative References .....................................7
80 Appendix A. Acknowledgements .......................................8
81 Appendix B. Examples ...............................................8
82 B.1. SPF DNS Record for Domain That Sends No Mail but
83 Requests Reports ...........................................8
84 B.2. Minimal SPF DNS Record Change to Add a Reporting
85 Address ....................................................8
86 B.3. SPF DNS Record with Reporting Address, Report
87 Percentage, and Requested Report Type ......................8
91 The Abuse Reporting Format [ARF] defines a message format for sending
92 reports of abuse in the messaging infrastructure, with an eye toward
93 automating both the generation and consumption of those reports.
95 The Sender Policy Framework [SPF] is one mechanism for message sender
96 authentication; it is "path-based", meaning it authenticates the
97 route that a message took from origin to destination. The output is
98 a verified domain name that can then be subjected to some sort of
99 evaluation process (e.g., comparison to a known-good list, submission
100 to a reputation service, etc.).
102 This document extends [SPF] to add an optional reporting address and
103 other parameters. Extension of [ARF] to add features required for
104 the reporting of these incidents is covered in [ARF-AUTHFAIL] and
107 This document additionally creates a an IANA registry of [SPF] record
108 modifiers to avoid modifier namespace collisions.
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116RFC 6652 SPF Auth Failure Reporting June 2012
123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
125 document are to be interpreted as described in [KEYWORDS].
1272.2. Imported Definitions
129 The [ABNF] token "qp-section" is defined in [MIME].
131 "local-part" is defined in [MAIL].
133 "addr-spec" is defined in [MAIL].
1353. Optional Reporting Address for SPF
137 There exist cases in which an ADministrative Management Domain (ADMD)
138 (see [EMAIL-ARCH]) employing [SPF] for announcing sending practices
139 may want to know when messages are received via unauthorized routing.
140 Currently, there is no such method defined in conjunction with
141 standardized approaches such as [ARF]. Similar information can be
142 gathered using a specially crafted [SPF] record and a special DNS
143 server to track [SPF] record lookups.
145 This document defines the following optional "modifier" (as defined
146 in Section 4.6.1 of [SPF]) to SPF records, using the form defined in
149 ra= Reporting Address (plain-text; OPTIONAL; no default). MUST be a
150 local-part (see Section 3.4.1 of [MAIL]) specifying an e-mail
151 address to which a report SHOULD be sent when mail claiming to
152 be from this domain (see Section 2.4 of [SPF] for a description
153 of how domains are identified for SPF checks) has failed the
154 evaluation algorithm described in [SPF], in particular because a
155 message arrived via an unauthorized route. To generate a
156 complete address to which the report is sent, the Verifier
157 simply appends to this value an "@" followed by the
158 SPF-compliant domain per Section 4.1 of [SPF]. ra= modifiers in
159 a record that was reached by following an "include" mechanism
160 (defined in Section 5.2 of [SPF]) MUST be ignored.
164 spf-report-tag = "ra=" qp-section
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172RFC 6652 SPF Auth Failure Reporting June 2012
175 rp= Requested Report Percentage (plain-text; OPTIONAL; default is
176 "100"). The value is an integer from 0 to 100 inclusive that
177 indicates what percentage of incidents of SPF failures, selected
178 at random, are to cause reports to be generated. The report
179 generator SHOULD NOT issue reports for more than the requested
180 percentage of incidents. An exception to this might be some
181 out-of-band arrangement between two parties to override it with
182 some mutually agreed value. Report generators MAY make use of
183 the "Incidents:" field in [ARF] to indicate that there are more
184 reportable incidents than there are reports.
188 spf-rp-tag = "rp=" 1*12DIGIT "/" 1*12DIGIT
190 rr= Requested Reports (plain-text; OPTIONAL; default is "all"). The
191 value MUST be a colon-separated list of tokens representing
192 those conditions under which a report is desired. See
193 Section 4.1 for a list of valid tags.
197 spf-rr-type = ( "all" / "e" / "f" / "s" / "n" )
199 spf-rr-tag = "rr=" spf-rr-type *( ":" spf-rr-type )
201 In the absence of an "ra=" tag in the SPF record, the "rp=" and "rr="
202 tags MUST be ignored, and the report generator MUST NOT issue a
207 This memo also includes, as the "rr" tokens defined above, the means
208 by which the sender can request reports for specific circumstances of
209 interest. Verifiers MUST NOT generate reports for incidents that do
210 not match a requested report and MUST ignore requests for reports not
211 included in this list.
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228RFC 6652 SPF Auth Failure Reporting June 2012
2314.1. Requested Reports for SPF Failures
233 The following report requests are defined for SPF results:
235 all All reports are requested.
237 e Reports are requested for messages that produced an SPF result
238 of "TempError" or "PermError".
240 f Reports are requested for messages that produced an SPF result
243 s Reports are requested for messages that produced an SPF result
246 n Reports are requested for messages that produced an SPF result
247 of "Neutral" or "None".
2495. IANA Considerations
251 As required by [IANA-CONS], this section contains registry
252 information for the new [SPF] modifiers.
2545.1. SPF Modifier Registration
256 IANA has created the Modifier Names registry under Sender Policy
257 Framework Parameters, to include a list of all registered SPF
258 modifier names and their defining documents.
260 New registrations or updates are to be published in accordance with
261 the "Specification Required" guidelines as described in [IANA-CONS].
262 New registrations and updates MUST contain the following information:
264 1. Name of the modifier being registered or updated
266 2. The document in which the specification of the modifier is
269 3. New or updated status, which MUST be one of the following:
271 Current: The field is in current use
273 Deprecated: The field might be in current use but its use is
276 Historic: The field is no longer in current use
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284RFC 6652 SPF Auth Failure Reporting June 2012
287 An update may make a notation on an existing registration indicating
288 that a registered field is historic or deprecated if appropriate.
290 +------------+-----------------+---------+
291 | MODIFIER | REFERENCE | STATUS |
292 +------------+-----------------+---------+
293 | exp | RFC 4408 | Current |
294 | redirect | RFC 4408 | Current |
295 | ra | (this document) | Current |
296 | rp | (this document) | Current |
297 | rr | (this document) | Current |
298 +------------+-----------------+---------+
3006. Security Considerations
302 Inherited considerations: implementers are advised to consider the
303 Security Considerations sections of [SPF], [ARF], [ARF-AS], and
306 In addition to the advice in the Security Considerations section of
307 [ARF-AS], these additional considerations apply to the generation of
308 [SPF] authentication failure reports:
3106.1. Identity Selection
312 Preventing an [SPF] failure for SPF authentication failure reports is
313 essential to mitigate the risk of data loops.
315 If the [SMTP] return address to be used will not be the NULL
316 return address, i.e., "MAIL FROM:<>", then the selected return
317 address MUST be selected such that it will pass [SPF] MAIL FROM
318 checks upon initial receipt.
320 If the report is passed to the Message Submission Agent (MSA) (MSA
321 is described in [EMAIL-ARCH] using [SMTP]), the HELO/EHLO command
322 parameter SHOULD also be selected so that it will pass [SPF] HELO
327 It is impossible to predict the volume of reports this facility will
328 generate when enabled by a report receiver. An implementer ought to
329 anticipate substantial volume, since the amount of abuse occurring at
330 receivers cannot be known ahead of time, and may vary rapidly and
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340RFC 6652 SPF Auth Failure Reporting June 2012
3457.1. Normative References
347 [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for
348 Syntax Specifications: ABNF", STD 68, RFC 5234,
351 [ARF] Shafranovich, Y., Levine, J., and M. Kucherawy, "An
352 Extensible Format for Email Feedback Reports", RFC 5965,
355 [ARF-AS] Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
356 Feedback Reports: An Applicability Statement for the Abuse
357 Reporting Format (ARF)", RFC 6650, June 2012.
360 Fontana, H., "Authentication Failure Reporting Using the
361 Abuse Reporting Format", RFC 6591, April 2012.
364 Narten, T. and H. Alvestrand, "Guidelines for Writing an
365 IANA Considerations Section in RFCs", BCP 26, RFC 5226,
368 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
369 Requirement Levels", BCP 14, RFC 2119, March 1997.
371 [MAIL] Resnick, P., Ed., "Internet Message Format", RFC 5322,
374 [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
375 Extensions (MIME) Part One: Format of Internet Message
376 Bodies", RFC 2045, November 1996.
378 [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
381 [SPF] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
382 for Authorizing Use of Domains in E-Mail, Version 1",
383 RFC 4408, April 2006.
3857.2. Informative References
388 Crocker, D., "Internet Mail Architecture", RFC 5598,
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396RFC 6652 SPF Auth Failure Reporting June 2012
399Appendix A. Acknowledgements
401 The author wishes to acknowledge the following for their review and
402 constructive criticism of this proposal: Murray Kucherawy, Tim
403 Draegen, Julian Mehnle, and John Levine.
407B.1. SPF DNS Record for Domain That Sends No Mail but Requests Reports
409 v=spf1 ra=postmaster -all
411B.2. Minimal SPF DNS Record Change to Add a Reporting Address
413 v=spf1 mx:example.org ra=postmaster -all
415B.3. SPF DNS Record with Reporting Address, Report Percentage, and
416 Requested Report Type
418 v=spf1 mx:example.org -all ra=postmaster rp=10 rr=e
425 Ellicott City, MD 21042
428 Phone: +1 301 325 5475
429 EMail: scott@kitterman.com
450Kitterman Standards Track [Page 8]