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rfc:rfc6650

Internet Engineering Task Force (IETF) J. Falk Request for Comments: 6650 Return Path Updates: 5965 M. Kucherawy, Ed. Category: Standards Track Cloudmark ISSN: 2070-1721 June 2012

            Creation and Use of Email Feedback Reports:
  An Applicability Statement for the Abuse Reporting Format (ARF)

Abstract

 RFC 5965 defines an extensible, machine-readable format intended for
 mail operators to report feedback about received email to other
 parties.  This applicability statement describes common methods for
 utilizing this format for reporting both abuse and authentication
 failure events.  Mailbox Providers of any size, mail-sending
 entities, and end users can use these methods as a basis to create
 procedures that best suit them.  Some related optional mechanisms are
 also discussed.

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 Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6650.

Falk & Kucherawy Standards Track [Page 1] RFC 6650 ARF AS June 2012

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 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.

Table of Contents

 1. Introduction ....................................................3
 2. Definitions .....................................................4
 3. Solicited and Unsolicited Reports ...............................4
 4. Generating and Handling Solicited Abuse Reports .................4
    4.1. General Considerations for Feedback Providers ..............4
    4.2. Where to Send Reports ......................................5
    4.3. What to Put in Reports .....................................5
    4.4. General Considerations for Feedback Consumers ..............5
    4.5. What to Expect .............................................6
    4.6. What to Do with Reports ....................................6
 5. Generating and Handling Unsolicited Abuse Reports ...............6
    5.1. General Considerations .....................................6
    5.2. When to Generate Reports ...................................7
    5.3. Where to Send Reports ......................................7
    5.4. What to Put in Reports .....................................8
    5.5. What to Do with Reports ....................................9
 6. Generating Automatic Authentication Failure Reports ............10
 7. Security Considerations ........................................11
    7.1. Security Considerations in Other Documents ................11
    7.2. Forgeries .................................................11
    7.3. Amplification Attacks .....................................11
    7.4. Automatic Generation ......................................11
    7.5. Reporting Multiple Incidents ..............................12
 8. Acknowledgements ...............................................13
 9. References .....................................................13
    9.1. Normative References ......................................13
    9.2. Informative References ....................................14

Falk & Kucherawy Standards Track [Page 2] RFC 6650 ARF AS June 2012

1. Introduction

 The Abuse Reporting Format (ARF) was initially developed for two very
 specific use cases.  Initially, it was intended to be used for
 reporting feedback between large email operators, or from large email
 operators to end user network access operators, any of whom could be
 presumed to have automated abuse-handling systems.  Secondarily, it
 is used by those same large mail operators to send those same reports
 to other entities, including those involved in sending bulk email for
 commercial purposes.  In either case, the reports would be triggered
 by direct end user action such as clicking on a "report spam" button
 in their email client.
 Though other uses for ARF as defined in [RFC5965] have been discussed
 (and may be documented similarly in the future), abuse reporting
 remains the primary application, with a small amount of adoption of
 extensions that enable authentication failure reporting.
 This applicability statement provides direction for using ARF in both
 contexts.  It also includes some statements about the use of ARF in
 conjunction with other email technologies.
 The purpose for reporting abusive messages is to stop recurrences.
 The methods described in this document focus on automating abuse
 reporting as much as practical, so as to minimize the work of a
 site's abuse team.  There are further reasons why abuse feedback
 generation is worthwhile, such as instruction of mail filters or
 reputation trackers, or initiation of investigations of particularly
 egregious abuses.  These other applications are not discussed in
 this memo.
 Further introduction to this topic may be found in [RFC6449], which
 has more information about the general topic of abuse reporting.
 Many of the specific ARF guidelines in this document were taken from
 the principles presented in [RFC6449].
 At the time of publication of this document, five feedback types are
 registered.  This document only discusses two of them ("abuse"
 [RFC5965] and "auth-failure" [RFC6591]), as they are seeing
 sufficient use in practice that applicability statements can be made
 about them.  The others, i.e., "fraud" [RFC5965], "other" [RFC5965],
 and "not-spam" [RFC6430], are either too new or too seldom used to be
 included here.

Falk & Kucherawy Standards Track [Page 3] RFC 6650 ARF AS June 2012

2. Definitions

 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 [RFC2119] and are
 intended to replace the Requirement Levels described in Section 3.3
 of [RFC2026].
 Some of the terminology used in this document is taken from
 [RFC5598].
 "Mailbox Provider" refers to an organization that accepts, stores,
 and offers access to [RFC5322] messages ("email messages") for end
 users.  Such an organization has typically implemented SMTP [RFC5321]
 and might provide access to messages through IMAP [RFC3501], the Post
 Office Protocol (POP) [RFC1939], a proprietary interface designed for
 HTTP [RFC2616], or a proprietary protocol.

3. Solicited and Unsolicited Reports

 The original, and still by far the most common, application of
 [RFC5965] is when two mail systems make a private agreement to
 exchange abuse reports -- usually reports due to recipients manually
 reporting messages as spam.  We refer to these as solicited reports.
 Other uses for ARF involve such reports sent between parties that
 don't know each other.  These unsolicited reports are sent without
 prior arrangement between the parties as to the context and meaning
 of the reports.  Therefore, the constraints on how these unsolicited
 reports need to be structured such that they are likely to be useful
 to the recipient -- e.g., to what address(es) they can usefully be
 sent, what issues they can be used to report, and how they can be
 handled by the receiver of the report -- are very different.
 The two cases are covered separately in the sections that follow.

4. Generating and Handling Solicited Abuse Reports

4.1. General Considerations for Feedback Providers

 A Mailbox Provider receives reports of abusive or unwanted mail from
 its users, most often by providing a "report spam" button (or similar
 nomenclature) in the MUA (Mail User Agent).  The method of
 transferring this message and any associated metadata from the MUA to
 the Mailbox Provider's ARF processing system is not defined by any
 standards document but is discussed further in Section 3.2 of
 [RFC6449].  Policy concerns related to the collection of this data
 are discussed in Section 3.4 of [RFC6449].

Falk & Kucherawy Standards Track [Page 4] RFC 6650 ARF AS June 2012

 To implement the recommendations of this memo, the reports are
 formatted per [RFC5965] and transmitted as an email message
 [RFC5322], typically using SMTP [RFC5321].
 Ongoing maintenance of an ARF processing system is discussed in
 Section 3.6 of [RFC6449].

4.2. Where to Send Reports

 The Mailbox Provider SHOULD NOT send reports to addresses that have
 not explicitly requested them.  A valid deviation might be the result
 of local policy instructions.  The process whereby such parties may
 request the reports is discussed in Section 3.5 of [RFC6449].

4.3. What to Put in Reports

 The reports SHOULD use "Feedback-Type: abuse" for the report type.
 Although a Mailbox Provider generating the reports can use other
 types appropriate to the nature of the abuse being reported, the
 operator receiving the reports might not treat different feedback
 types differently.
 The following fields are optional in [RFC5965] but SHOULD be used in
 this context when their corresponding values are available:
 Original-Mail-From, Arrival-Date, Source-IP, and Original-Rcpt-To.
 Other optional fields can be included as deemed appropriate by the
 implementer.
 User-identifiable data MAY be obscured as described in [RFC6590].

4.4. General Considerations for Feedback Consumers

 ARF report streams are established proactively between Feedback
 Providers and Feedback Consumers.  Recommendations for preparing to
 request feedback are discussed in Section 4.1 of [RFC6449].
 Operators MUST be able to accept ARF [RFC5965] reports as email
 messages [RFC5322] over SMTP [RFC5321].  These messages, and other
 types of email messages that can be received, are discussed in
 Section 4.2 of [RFC6449].
 Recipients of feedback reports that are part of formal feedback
 arrangements have to be capable of handling large volumes of reports.
 This could require automation of report processing as discussed in
 Section 4.4 of [RFC6449].

Falk & Kucherawy Standards Track [Page 5] RFC 6650 ARF AS June 2012

4.5. What to Expect

 The list of valid Feedback-Types is defined in [RFC5965], which
 created an IANA registry for valid values to allow for extensions.
 However, to allow for handling of new types that are not yet
 supported, an automated report processing system MUST NOT reject (in
 the SMTP sense) a report based solely on an unknown Feedback-Type.
 The automated system can simply set reports of unknown types aside
 for manual handling.  However, Mailbox Providers might only make use
 of the "abuse" Feedback-Type.  Therefore, report receivers might be
 required to do additional analysis to separate different types of
 abuse reports after receipt if they do not have prior specific
 knowledge of the sender of the report.
 Report receivers MUST accept reports that have obscured their user-
 identifiable data as described in [RFC6590].  That document also
 discusses the handling of such reports.  This technique is also
 discussed in Section 4.4 of [RFC6449].

4.6. What to Do with Reports

 Section 4.3 of [RFC6449] discusses actions that mail operators might
 take upon receiving a report (or multiple reports).

5. Generating and Handling Unsolicited Abuse Reports

5.1. General Considerations

 It is essential for report recipients to be capable of throttling
 reports being sent to avoid damage to their own installations.
 Therefore, Feedback Providers MUST provide a way for report
 recipients to request that no further reports be sent.
 Unfortunately, no standardized mechanism for such requests exists to
 date, and all existing mechanisms for meeting this requirement are
 out-of-band.
 Message authentication is generally a good idea, but it is especially
 important to encourage credibility of, and thus response to,
 unsolicited reports.  Therefore, as with any other message, Feedback
 Providers sending unsolicited reports SHOULD send reports that they
 expect will pass the Sender Policy Framework (SPF) [RFC4408] and/or
 DomainKeys Identified Mail (DKIM) [RFC6376] checks.

Falk & Kucherawy Standards Track [Page 6] RFC 6650 ARF AS June 2012

5.2. When to Generate Reports

 Handling of unsolicited reports has a significant cost to the report
 receiver.  Senders of unsolicited reports, especially those sending
 large volumes of them automatically, SHOULD NOT send reports that
 cannot be used as a basis for action by the recipient, whether this
 is due to the report being sent about an incident that is not abuse-
 related, the report being sent to an email address that won't result
 in action, or the content or format of the report being hard for the
 recipient to read or use.
 Feedback Providers SHOULD NOT report all mail sent from a particular
 sender merely because some of it is determined to be abusive.
 Mechanical reports of mail that "looks like" spam, based solely on
 the results of inline content analysis tools, SHOULD NOT be sent
 since, because of their subjective nature, they are unlikely to
 provide a basis for the recipient to take action.  Complaints
 generated by end users about mail that is determined by them to be
 abusive, or mail delivered to "spam trap" or "honeypot" addresses,
 are far more likely to be accurate and MAY be sent.
 If a Feedback Provider applies SPF [RFC4408] to arriving messages, a
 report SHOULD NOT be generated to the RFC5321.MailFrom domain if the
 SPF evaluation produced a "Fail", "SoftFail", "TempError", or
 "PermError" report, as no reliable assertion or assumption can be
 made that use of the domain was authorized.  A valid exception would
 be specific knowledge that the SPF result is not definitive for that
 domain under those circumstances (for example, a message that is also
 signed using DKIM [RFC6376] by the same domain, and that signature
 validates).

5.3. Where to Send Reports

 Rather than generating feedback reports themselves, MUAs SHOULD
 create abuse reports and send these reports back to their Mailbox
 Providers so that they can generate and send ARF messages on behalf
 of end users (see Section 3.2 of [RFC6449]).  This allows centralized
 processing and tracking of reports, and provides training input to
 filtering systems.  There is, however, no standard mechanism for this
 signaling between MUAs and Mailbox Providers to trigger abuse
 reports.
 Feedback Providers SHOULD NOT send reports to recipients that are
 uninvolved or only peripherally involved.  For example, they SHOULD
 NOT send reports to the operator of every Autonomous System in the
 path between the apparent originating system and the operator

Falk & Kucherawy Standards Track [Page 7] RFC 6650 ARF AS June 2012

 generating the report.  Instead, they need to send reports to
 recipients that are both responsible for the messages and able to do
 something about them.
 Deciding where to send an unsolicited report will typically rely on
 heuristics.  Abuse addresses in WHOIS [RFC3912] records of the IP
 address relaying the subject message and/or of the domain name found
 in the results of a PTR ("reverse lookup") query on that address are
 likely reasonable candidates, as is the abuse@domain role address
 (see [RFC2142]) of related domains.  Unsolicited reports SHOULD NOT
 be sent to email addresses that are not clearly intended to handle
 abuse reports.  Legitimate candidates include those found in WHOIS
 records or on a web site that either are explicitly described as an
 abuse contact or are of the form "abuse@domain".
 Where an abusive message is authenticated using a domain-level
 authentication technology such as DKIM [RFC6376] or SPF [RFC4408],
 the domain that has been verified by the authentication mechanism is
 often a reasonable candidate for receiving feedback about the
 message.  For DKIM, though, while the authenticated domain has some
 responsibility for the mail sent, it can be a poor contact point for
 abuse issues (for example, it could represent the message's author
 but not its sender, it could identify the bad actor responsible for
 the message, or it could refer to a domain that cannot receive mail
 at all).
 Often, unsolicited reports will have no meaning if sent to abuse
 reporting addresses belonging to the abusive parties themselves.  In
 fact, it is possible that such reports might reveal information about
 complainants.  Reports SHOULD NOT be sent to such addresses if they
 can be identified beforehand, except where the abusive party is known
 to be responsive to such reports.

5.4. What to Put in Reports

 Reports SHOULD use "Feedback-Type: abuse" but can use other types as
 appropriate.  However, the Mailbox Provider generating the reports
 cannot assume that the operator receiving the reports will treat
 different Feedback-Types differently.
 Reports SHOULD include the following optional fields whenever their
 corresponding values are available and applicable to the report:
 Original-Mail-From, Arrival-Date, Source-IP, and Original-Rcpt-To.
 Other optional fields can be included as deemed appropriate by the
 implementer.

Falk & Kucherawy Standards Track [Page 8] RFC 6650 ARF AS June 2012

 Experience suggests that the use of ARF is advisable in most
 contexts.  Automated recipient systems can handle abuse reports sent
 in ARF at least as well as any other format such as plain text, with
 or without a copy of the message attached.  That holds even for
 systems that did not request ARF reports, assuming such reports are
 generated considering the possibility of recipients that don't use
 automated ARF parsing.  Anyone sending unsolicited reports in ARF can
 legitimately presume that some recipients will only be able to access
 the human-readable (first, text/plain) part of it and SHOULD include
 all information needed also in this part.  Further, they SHOULD
 ensure that the report is readable when viewed as plain text, to give
 low-end ticketing systems as much assistance as possible.  In extreme
 cases, failure to take these steps may result in the report being
 discarded or ignored.

5.5. What to Do with Reports

 Receivers of unsolicited reports can take advantage of the
 standardized parts of ARF to automate processing.  Independent of the
 sender of the report, they can improve processing by separating valid
 reports from invalid reports by, for example, looking for references
 to IP address ranges, domains, and mailboxes for which the recipient
 organization is responsible in the copy of the reported message, and
 by correlating multiple reports of similar messages to identify bulk
 email senders.
 Per Section 4.4 of [RFC6449], a network service provider MAY use ARF
 data for automated forwarding of feedback messages to the originating
 customer.
 Published abuse mailbox addresses SHOULD NOT reject non-ARF messages
 based solely on the format, as generation of ARF messages can
 occasionally be unavailable or not applicable.  Deviation from this
 requirement could be done due to local policy decisions regarding
 other message criteria.
 Although [RFC6449] suggests that replying to feedback is not useful,
 in the case of receipt of ARF reports where no feedback arrangement
 has been established, a non-automated reply might be desirable to
 indicate what action resulted from the complaint, heading off more
 severe filtering by the Feedback Provider.  In addition, using an
 address that cannot receive replies precludes any requests for
 additional information and increases the likelihood that further
 reports will be discarded or blocked.  Thus, a Feedback Provider
 sending unsolicited reports SHOULD NOT generate reports for which a
 reply cannot be received.  Where an unsolicited report results in the
 establishment of contact with a responsible and responsive party,
 this data can be saved for future complaint handling and possible

Falk & Kucherawy Standards Track [Page 9] RFC 6650 ARF AS June 2012

 establishment of a formal (solicited) feedback arrangement.  See
 Section 3.5 of [RFC6449] for a discussion of establishment of
 feedback arrangements.

6. Generating Automatic Authentication Failure Reports

 There are some cases where report generation is caused by automation
 rather than user requests.  A specific example of this is reporting,
 using ARF (or extensions to it), of messages that fail particular
 message authentication checks.  Examples of this include [RFC6651]
 and [RFC6652].  The considerations presented below apply in those
 cases.
 The applicability statement for this use case is somewhat smaller, as
 many of the issues associated with abuse reports are not relevant to
 reports about authentication failures.
 Automatic feedback generators MUST select actual message recipients
 based on data provided by willing report receivers.  In particular,
 recipients MUST NOT be selected using heuristics.
 If the message under evaluation by the Verifier is an ARF [RFC5965]
 message, a report MUST NOT be automatically generated.
 The message for a new report sent via SMTP MUST be constructed so as
 to avoid amplification attacks, deliberate or otherwise.  The
 envelope sender address of the report MUST be chosen so that these
 reports will not generate mail loops.  Similar to Section 2 of
 [RFC3464], the envelope sender address of the report MUST be chosen
 to ensure that no feedback reports will be issued in response to the
 report itself.  Therefore, when an SMTP transaction is used to send a
 report, the MAIL FROM command SHOULD use the NULL reverse-path, i.e.,
 "MAIL FROM:<>".  An exception to this would be the use of a reverse-
 path selected such that SPF checks on the report will pass; in such
 cases, the operator will need to make provisions to avoid the
 amplification attack or mail loop via other means.
 Reports SHOULD use "Feedback-Type: auth-failure" but MAY use other
 types as appropriate.  However, the Mailbox Provider generating the
 reports cannot assume that the operator receiving the reports will
 treat different Feedback-Types differently.
 These reports SHOULD include the following fields, although they are
 optional in [RFC5965], whenever their corresponding values are
 available: Original-Mail-From, Arrival-Date, Source-IP, and
 Original-Rcpt-To.  Other optional fields can be included as deemed
 appropriate by the implementer.

Falk & Kucherawy Standards Track [Page 10] RFC 6650 ARF AS June 2012

7. Security Considerations

7.1. Security Considerations in Other Documents

 Implementers are strongly urged to review, at a minimum, the Security
 Considerations sections of [RFC5965] and [RFC6449].

7.2. Forgeries

 Feedback Providers that relay user complaints directly, rather than
 by reference to a stored message (e.g., IMAP or POP), could be duped
 into sending a complaint about a message that the complaining user
 never actually received, as an attack on the purported originator of
 the falsified message.  Feedback Providers need to be resilient to
 such attack methods.
 Also, these reports may be forged as easily as ordinary Internet
 electronic mail.  User agents and automatic mail handling facilities
 (such as mail distribution list exploders) that wish to make
 automatic use of reports of any kind should take appropriate
 precautions to minimize the potential damage from denial-of-service
 attacks.
 Perhaps the simplest means of mitigating this threat is to assert
 that these reports should themselves be signed with something like
 DKIM and/or authorized by something like SPF.  Note, however, that if
 there is a problem with the email infrastructure at either end, DKIM
 and/or SPF may result in reports that aren't trusted or even accepted
 by their intended recipients, so it is important to make sure those
 components are properly configured.  The use of both technologies in
 tandem can resolve this concern to a degree, since they generally
 have disjoint failure modes.

7.3. Amplification Attacks

 Failure to comply with the recommendations regarding selection of the
 envelope sender can lead to amplification denial-of-service attacks.
 This is discussed in Section 6 as well as in [RFC3464].

7.4. Automatic Generation

 ARF [RFC5965] reports have historically been generated individually
 as a result of some kind of human request, such as someone clicking a
 "Report Abuse" button in a mail reader.  In contrast, the mechanisms
 described in some extension documents (i.e., [RFC6651] and [RFC6652])
 are focused around automated reporting.  This obviously implies the

Falk & Kucherawy Standards Track [Page 11] RFC 6650 ARF AS June 2012

 potential for much larger volumes or higher frequency of messages,
 and thus greater mail system load (both for Feedback Providers and
 report receivers).
 Those mechanisms are primarily intended for use in generating reports
 to aid implementers of DKIM [RFC6376], Author Domain Signing
 Practices (ADSP) [RFC5617], and SPF [RFC4408], and other related
 protocols during development and debugging.  They are not generally
 intended for prolonged forensic use, specifically because of these
 load concerns.  However, extended use is possible by ADministrative
 Management Domains (ADMDs) that want to keep a close watch for fraud
 or infrastructure problems.  It is important to consider the impact
 of doing so on both Feedback Providers and the requesting ADMDs.
 A sender requesting these reports can cause its mail servers to be
 overwhelmed if it sends out signed messages whose signatures fail to
 verify for some reason, provoking a large number of reports from
 Feedback Providers.  Similarly, a Feedback Provider could be
 overwhelmed by a large volume of messages requesting reports whose
 signatures fail to validate, as the Feedback Provider now needs to
 send reports back to the Signer.
 Limiting the rate of generation of these messages may be appropriate
 but threatens to inhibit the distribution of important and possibly
 time-sensitive information.
 In general ARF feedback loop terms, it is often suggested that
 Feedback Providers only create these (or any) ARF reports after an
 out-of-band arrangement has been made between two parties.  These
 extension mechanisms provide ways to adjust parameters of an
 authorized abuse report feedback loop that is configured and
 activated by private agreement.  The alternative (sending reports
 automatically based solely on data found in the messages) may have
 unintended consequences.

7.5. Reporting Multiple Incidents

 If it is known that a particular host generates abuse reports upon
 certain incidents, an attacker could forge a high volume of messages
 that will trigger such a report.  The recipient of the report could
 then be inundated with reports.  This could easily be extended to a
 distributed denial-of-service attack by finding a number of report-
 generating servers.
 The incident count referenced in ARF [RFC5965] provides a limited
 form of mitigation.  The host that generates reports can elect to
 send reports only periodically, with each report representing a
 number of identical or nearly identical incidents.  One might even do

Falk & Kucherawy Standards Track [Page 12] RFC 6650 ARF AS June 2012

 something inverse-exponentially, sending reports for each of the
 first ten incidents, then every tenth incident up to 100, then every
 100th incident up to 1000, etc., until some period of relative quiet
 after which the limitation resets.
 The use of this technique for "nearly identical" incidents in
 particular causes a degradation in reporting quality, however.  If
 for example a large number of pieces of spam arrive from one
 attacker, a reporting agent could decide only to send a report about
 a fraction of those messages.  While this averts a flood of reports
 to a system administrator, the precise details of each incident are
 similarly not sent.
 Other rate-limiting provisions might be considered, such as detecting
 a temporary failure response from the report destination and thus
 halting report generation to that destination for some period, or
 simply imposing or negotiating a hard limit on the number of reports
 to be sent to a particular receiver in a given time frame.

8. Acknowledgements

 The author and editor wish to thank Steve Atkins, John Levine, Shmuel
 Metz, S. Moonesamy, and Alessandro Vesely for their contributions to
 this memo.
 All of the best practices referenced by this document are found in
 [RFC6449], written within the Collaboration Committee of the
 Messaging Anti-Abuse Working Group (MAAWG).
 Finally, the original author wishes to thank the doctors and staff
 at the University of Texas MD Anderson Cancer Center for doing what
 they do.

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
            October 2008.
 [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
            October 2008.
 [RFC5598]  Crocker, D., "Internet Mail Architecture", RFC 5598,
            July 2009.

Falk & Kucherawy Standards Track [Page 13] RFC 6650 ARF AS June 2012

 [RFC5965]  Shafranovich, Y., Levine, J., and M. Kucherawy, "An
            Extensible Format for Email Feedback Reports", RFC 5965,
            August 2010.
 [RFC6591]  Fontana, H., "Authentication Failure Reporting Using the
            Abuse Reporting Format", RFC 6591, April 2012.

9.2. Informative References

 [RFC1939]  Myers, J. and M. Rose, "Post Office Protocol - Version 3",
            STD 53, RFC 1939, May 1996.
 [RFC2026]  Bradner, S., "The Internet Standards Process --
            Revision 3", BCP 9, RFC 2026, October 1996.
 [RFC2142]  Crocker, D., "Mailbox Names for Common Services, Roles and
            Functions", RFC 2142, May 1997.
 [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
            Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
            Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
 [RFC3464]  Moore, K. and G. Vaudreuil, "An Extensible Message Format
            for Delivery Status Notifications", RFC 3464,
            January 2003.
 [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
            VERSION 4rev1", RFC 3501, March 2003.
 [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,
            September 2004.
 [RFC4408]  Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
            for Authorizing Use of Domains in E-Mail, Version 1",
            RFC 4408, April 2006.
 [RFC5617]  Allman, E., Fenton, J., Delany, M., and J. Levine,
            "DomainKeys Identified Mail (DKIM) Author Domain Signing
            Practices (ADSP)", RFC 5617, August 2009.
 [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
            "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376,
            September 2011.
 [RFC6430]  Li, K. and B. Leiba, "Email Feedback Report Type Value:
            not-spam", RFC 6430, November 2011.

Falk & Kucherawy Standards Track [Page 14] RFC 6650 ARF AS June 2012

 [RFC6449]  Falk, J., Ed., "Complaint Feedback Loop Operational
            Recommendations", RFC 6449, November 2011.
 [RFC6590]  Falk, J., Ed., and M. Kucherawy, Ed., "Redaction of
            Potentially Sensitive Data from Mail Abuse Reports",
            RFC 6590, April 2012.
 [RFC6651]  Kucherawy, M., "Extensions to DomainKeys Identified Mail
            (DKIM) for Failure Reporting", RFC 6651, June 2012.
 [RFC6652]  Kitterman, S., "Sender Policy Framework (SPF)
            Authentication Failure Reporting Using the Abuse Reporting
            Format", RFC 6652, June 2012.

Authors' Addresses

 J.D. Falk
 Return Path
 100 Mathilda Place, Suite 100
 Sunnyvale, CA  94086
 USA
 URI:   http://www.returnpath.net/
 Murray S. Kucherawy (editor)
 Cloudmark
 128 King St., 2nd Floor
 San Francisco, CA  94107
 US
 EMail: superuser@gmail.com

Falk & Kucherawy Standards Track [Page 15]

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