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Internet Engineering Task Force (IETF)                      S. KittermanRequest for Comments: 6652                                         AgariUpdates:4408                                                  June 2012Category: Standards TrackISSN: 2070-1721Sender Policy Framework (SPF) Authentication Failure ReportingUsing the Abuse Reporting FormatAbstract   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 updatesRFC 4408 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6652.Copyright Notice   Copyright (c) 2012 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) 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.Kitterman                    Standards Track                    [Page 1]

RFC 6652               SPF Auth Failure Reporting              June 2012Table of Contents1. Introduction ....................................................22. Definitions .....................................................32.1. Key Words ..................................................32.2. Imported Definitions .......................................33. Optional Reporting Address for SPF ..............................34. Requested Reports ...............................................44.1. Requested Reports for SPF Failures .........................55. IANA Considerations .............................................55.1. SPF Modifier Registration ..................................56. Security Considerations .........................................66.1. Identity Selection .........................................66.2. Report Volume ..............................................67. References ......................................................77.1. Normative References .......................................77.2. Informative References .....................................7Appendix A. Acknowledgements .......................................8Appendix B. Examples ...............................................8      B.1. SPF DNS Record for Domain That Sends No Mail but           Requests Reports ...........................................8      B.2. Minimal SPF DNS Record Change to Add a Reporting           Address ....................................................8      B.3. SPF DNS Record with Reporting Address, Report           Percentage, and Requested Report Type ......................81.  Introduction   The Abuse Reporting Format [ARF] 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 [SPF] 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 [SPF] to add an optional reporting address and   other parameters.  Extension of [ARF] to add features required for   the reporting of these incidents is covered in [ARF-AUTHFAIL] and   [ARF-AS].   This document additionally creates a an IANA registry of [SPF] record   modifiers to avoid modifier namespace collisions.Kitterman                    Standards Track                    [Page 2]

RFC 6652               SPF Auth Failure Reporting              June 20122.  Definitions2.1.  Key Words   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 [KEYWORDS].2.2.  Imported Definitions   The [ABNF] token "qp-section" is defined in [MIME].   "local-part" is defined in [MAIL].   "addr-spec" is defined in [MAIL].3.  Optional Reporting Address for SPF   There exist cases in which an ADministrative Management Domain (ADMD)   (see [EMAIL-ARCH]) employing [SPF] 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 [ARF].  Similar information can be   gathered using a specially crafted [SPF] record and a special DNS   server to track [SPF] record lookups.   This document defines the following optional "modifier" (as defined   in Section 4.6.1 of [SPF]) 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 [MAIL]) 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 [SPF] for a description        of how domains are identified for SPF checks) has failed the        evaluation algorithm described in [SPF], 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 [SPF].  ra= modifiers in        a record that was reached by following an "include" mechanism        (defined in Section 5.2 of [SPF]) MUST be ignored.      ABNF:      spf-report-tag = "ra=" qp-sectionKitterman                    Standards Track                    [Page 3]

RFC 6652               SPF Auth Failure Reporting              June 2012   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 [ARF] 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.  SeeSection 4.1 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.4.  Requested Reports   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.Kitterman                    Standards Track                    [Page 4]

RFC 6652               SPF Auth Failure Reporting              June 20124.1.  Requested Reports for SPF Failures   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".5.  IANA Considerations   As required by [IANA-CONS], this section contains registry   information for the new [SPF] modifiers.5.1.  SPF Modifier Registration   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 [IANA-CONS].   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 useKitterman                    Standards Track                    [Page 5]

RFC 6652               SPF Auth Failure Reporting              June 2012   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        |RFC 4408        | Current |                 | redirect   |RFC 4408        | Current |                 | ra         | (this document) | Current |                 | rp         | (this document) | Current |                 | rr         | (this document) | Current |                 +------------+-----------------+---------+6.  Security Considerations   Inherited considerations: implementers are advised to consider the   Security Considerations sections of [SPF], [ARF], [ARF-AS], and   [ARF-AUTHFAIL].   In addition to the advice in the Security Considerations section of   [ARF-AS], these additional considerations apply to the generation of   [SPF] authentication failure reports:6.1.  Identity Selection   Preventing an [SPF] failure for SPF authentication failure reports is   essential to mitigate the risk of data loops.      If the [SMTP] 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 [SPF] MAIL FROM      checks upon initial receipt.      If the report is passed to the Message Submission Agent (MSA) (MSA      is described in [EMAIL-ARCH] using [SMTP]), the HELO/EHLO command      parameter SHOULD also be selected so that it will pass [SPF] HELO      checks.6.2.  Report Volume   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.Kitterman                    Standards Track                    [Page 6]

RFC 6652               SPF Auth Failure Reporting              June 20127.  References7.1.  Normative References   [ABNF]     Crocker, D., Ed., and P. Overell, "Augmented BNF for              Syntax Specifications: ABNF", STD 68,RFC 5234,              January 2008.   [ARF]      Shafranovich, Y., Levine, J., and M. Kucherawy, "An              Extensible Format for Email Feedback Reports",RFC 5965,              August 2010.   [ARF-AS]   Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email              Feedback Reports: An Applicability Statement for the Abuse              Reporting Format (ARF)",RFC 6650, June 2012.   [ARF-AUTHFAIL]              Fontana, H., "Authentication Failure Reporting Using the              Abuse Reporting Format",RFC 6591, April 2012.   [IANA-CONS]              Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 5226,              May 2008.   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [MAIL]     Resnick, P., Ed., "Internet Message Format",RFC 5322,              October 2008.   [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail              Extensions (MIME) Part One: Format of Internet Message              Bodies",RFC 2045, November 1996.   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol",RFC 5321,              October 2008.   [SPF]      Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)              for Authorizing Use of Domains in E-Mail, Version 1",RFC 4408, April 2006.7.2.  Informative References   [EMAIL-ARCH]              Crocker, D., "Internet Mail Architecture",RFC 5598,              July 2009.Kitterman                    Standards Track                    [Page 7]

RFC 6652               SPF Auth Failure Reporting              June 2012Appendix A.  Acknowledgements   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.Appendix B.  ExamplesB.1.  SPF DNS Record for Domain That Sends No Mail but Requests Reports   v=spf1 ra=postmaster -allB.2.  Minimal SPF DNS Record Change to Add a Reporting Address   v=spf1 mx:example.org ra=postmaster -allB.3.  SPF DNS Record with Reporting Address, Report Percentage, and      Requested Report Type   v=spf1 mx:example.org -all ra=postmaster rp=10 rr=eAuthor's Address   Scott Kitterman   Agari   3611 Scheel Dr.   Ellicott City, MD  21042   US   Phone: +1 301 325 5475   EMail: scott@kitterman.comKitterman                    Standards Track                    [Page 8]