Individual submission Y. Shafranovich Internet-Draft ShafTek Enterprises Intended status: Standards Track J. Levine Expires: April 22, 2010 Domain Assurance Council M. Kucherawy Cloudmark October 19, 2009 An Extensible Format for Email Feedback Reports draft-shafranovich-feedback-report-08 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 22, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the Shafranovich, et al. Expires April 22, 2010 [Page 1] Internet-Draft Format for Feedback Reports October 2009 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Shafranovich, et al. Expires April 22, 2010 [Page 2] Internet-Draft Format for Feedback Reports October 2009 Abstract This document defines an extensible format and MIME type that may be used by network operators to report feedback about received email to other parties. This format is intended as a machine-readable replacement for various existing report formats currently used in Internet email. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.2. E-mail Specific . . . . . . . . . . . . . . . . . . . 5 2. Format of Email Feedback Reports . . . . . . . . . . . . . . . 6 3. The 'message/feedback-report' Content Type . . . . . . . . . . 7 3.1. Required Fields . . . . . . . . . . . . . . . . . . . . . 7 3.2. Optional Fields Appearing Once . . . . . . . . . . . . . . 8 3.3. Optional Fields Appearing Multiple Times . . . . . . . . . 9 3.4. Formal Definition . . . . . . . . . . . . . . . . . . . . 9 4. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 13 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 5.1. MIME Type Registration of 'message/feedback-report' . . . 14 5.2. Feedback Report Header Fields . . . . . . . . . . . . . . 15 5.3. Feedback Report Type Values . . . . . . . . . . . . . . . 18 5.4. Feedback Report DKIM Failure Values . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 22 6.1. Inherited from RFC3462 . . . . . . . . . . . . . . . . . . 22 6.2. Interpretation . . . . . . . . . . . . . . . . . . . . . . 22 6.3. Envelope Sender Selection . . . . . . . . . . . . . . . . 22 6.4. Attacks Against Authentication Methods . . . . . . . . . . 22 6.5. Intentionally Malformed Reports . . . . . . . . . . . . . 23 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.1. Normative References . . . . . . . . . . . . . . . . . . . 24 7.2. Informative References . . . . . . . . . . . . . . . . . . 24 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 26 Appendix B. Sample Feedback Reports . . . . . . . . . . . . . . . 27 B.1. Simple Report for Email Abuse without Optional Headers . . 27 B.2. Opt-Out Report without Message Body . . . . . . . . . . . 29 B.3. Full Report for Email Abuse with All Headers . . . . . . . 30 B.4. Sample DKIM Failure Report . . . . . . . . . . . . . . . . 31 Appendix C. Public Discussion, History and Support . . . . . . . 32 Appendix D. Document History . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Shafranovich, et al. Expires April 22, 2010 [Page 3] Internet-Draft Format for Feedback Reports October 2009 1. Introduction As the spam problem continues to expand and potential solutions evolve, network operators are increasingly exchanging abuse reports among themselves and other parties. However, different operators have defined their own formats, and thus the receivers of these reports are forced to write custom software to interpret each. In addition, many operators use various other report formats to provide non-abuse-related feedback about processed email. This memo seeks to define a standard extensible format by creating the "message/ feedback-report" [MIME] type for these reports. This format and content type are intended to be used within the scope of the framework of the "multipart/report" content type defined in [REPORT]. While there has been previous work in this area (e.g. [STRADS-BCP] and [ASRG-ABUSE]), none of them have yet been successful. It is hoped that this document will have a better fate. This format is intended primarily as an Abuse Reporting Format (ARF) for reporting email abuse but also includes support for direct feedback via end user mail clients, reports of some types of virus activity, and some similar issues. It also has the capacity to support message authentication failure reporting, in particular [DKIM]. This document only defines the format and [MIME] content type to be used for these reports. Determination of where these reports should be sent, how trust among report generators and report recipients is established, and reports related to more than one message are outside the scope of this document. It is assumed that best practices will evolve over time, and will be codified in future documents. 1.1. Purpose The reports defined in this document are intended for several purposes: o To inform ISPs about email abuse originating from or related to their networks; o To inform email service providers or other primarily outbound senders that there may be issues regarding their mail; these issues include (but are not limited to) reports that the mail may be considered to be "spam" by a recipient of the message; o To inform email service provides about opt-out requests; Shafranovich, et al. Expires April 22, 2010 [Page 4] Internet-Draft Format for Feedback Reports October 2009 o To advise providers that certify or otherwise make assertions about mail of recipient disagreement with the assertions. Please note that while the parent "multipart/report" content type defined in [REPORT] is used for all kinds of administrative messages, this format is intended specifically for communications among providers regarding email abuse and related issues, and SHOULD NOT be used for other reports. 1.2. Requirements The following requirements are necessary for feedback reports (the actual specification is defined later in this document): o They must be both human and machine readable; o A copy of the original email message (both body and header) or the message header must be enclosed in order to allow the receiver to handle the report properly; o The machine readable section must provide ability for the report generators to share meta-data with receivers; o The format must be extensible. 1.3. Definitions This section defines various terms used throughout this document. 1.3.1. General 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]. 1.3.2. E-mail Specific See [I-D.DRAFT-CROCKER-EMAIL-ARCH] for further discussion on e-mail system architecture. Shafranovich, et al. Expires April 22, 2010 [Page 5] Internet-Draft Format for Feedback Reports October 2009 2. Format of Email Feedback Reports To satisfy the requirements, an email feedback report is defined as a [MIME] message with a top-level MIME content type of "multipart/ report" (as defined in [REPORT]). The following apply: a. The "report-type" parameter of the "multipart/report" type is set to "feedback-report"; b. The first MIME part of the message contains a human readable description of the report and MUST be included. c. The second MIME part of the message is a machine-readable section with the content type of "message/feedback-report" (defined later in this memo) and MUST be included. This section is intended to convey meta-data about the report in question that may not be readily available from the included email message itself. d. The third MIME part of the message is either of type "message/ rfc822" (as defined in [MIME-TYPES] and contains the original message in its entirety, OR is of type "text/rfc822-headers" (as defined in [REPORT] and contains a copy of the entire header block from the orignal message. This part MUST be included (contrary to [REPORT]). While some operators may choose to modify or redact this portion for privacy or legal reasons, it is RECOMMENDED that the entire original email message be included without any modification as such modifications can impede forensic work by the recipient of this report. e. Except as discussed below, each feedback report MUST be related to only a single email message. Summary and aggregate formats are outside of the scope of this specification. f. The Subject header field of the feedback report SHOULD be the same as the included email message about which the report is being generated and MAY include only the standard forwarding prefix used by MUAs such as "FW:". (Many smaller operators using MUAs for abuse handling rely on the subject lines for processing.) Shafranovich, et al. Expires April 22, 2010 [Page 6] Internet-Draft Format for Feedback Reports October 2009 3. The 'message/feedback-report' Content Type A new [MIME] content type called "message/feedback-report" is defined. This content type provides a machine-readable section intended to let the report generator convey meta-data to the report receiver. The intent of this section is to convey information which may not be obvious or may not be easily extracted from the original email message or headers. The body of this content type consists of multiple "fields" formatted according to the ABNF of [MAIL] header fields. This section defines the initial set of fields provided by this specification. Additional fields may be registered according to the procedure described later in this memo. Although these fields have a syntax similar to those of mail message header fields, they are semantically distinct; hence they SHOULD NOT be repeated in the header area of the message containing the report. Note that these fields represent information that the receiver is asserting about the report in question, but are not necessarily verifiable. Report receivers MUST NOT assume that these assertions are always accurate. 3.1. Required Fields The following report header fields are REQUIRED and MUST only appear once: o "Feedback-Type" contains the type of feedback report (as defined in the corresponding IANA registry and later in this memo). This is intended to let report parsers distinguish among different types of reports. o "User-Agent" indicates the name and version of the software program that generated the report. The format of this field MUST follow section 14.43 of [HTTP]. This field is for documentation only; there is no registry of user agent names or versions, and report receivers SHOULD NOT expect user agent names to belong to a known set. o "Version" indicates the version of specification that the report generator is using to generate the report. The version number in this specification is set to "0.1". [NOTE TO RFC EDITOR: This should be changed to "1" at time of publication.] The following report header fields MUST appear exactly once in a [DKIM] failure report (defined below) and MUST NOT appear in other reports: Shafranovich, et al. Expires April 22, 2010 [Page 7] Internet-Draft Format for Feedback Reports October 2009 o "DKIM-Failure" names the type of DKIM verification failure that occurred. 3.2. Optional Fields Appearing Once The following header fields are OPTIONAL and MUST NOT appear more than once: o "Original-Envelope-Id" contains the envelope ID string used in the original [SMTP] transaction (see section 2.2.1 of [DSN]). o "Original-Mail-From" contains a copy of the email address used in the MAIL FROM portion of the original SMTP transaction. The format of this field is defined in section 4.1.1.2 of [SMTP]. o "Arrival-Date" indicates the date and time at which the original message was received by recipient system's MTA. This field MUST be formatted as per section 3.3 of [MAIL]. o "Reporting-MTA" indicates the name of the MTA generating this feedback report. This field is defined in section 2.2.2 of [DSN], except that it is an optional field in this report. o "Source-IP" contains an IPv4 or IPv6 address of the MTA from which the original message was received. Addresses MUST be formatted as per section 4.1.3 of [SMTP]. o "Incidents" contains an integer indicating the number of incidents this report represents. The absence of this field implies the report covers a single incident. This field MUST NOT be used for report types other than "dkim". The historic field "Received-Date" SHOULD also be accepted and interpreted identically to "Arrival-Date". The following header fields are OPTIONAL and may each appear once in a [DKIM] failure report: o "DKIM-Canonicalized-Body" contains the canonicalized message body of a message which failed DKIM verification, base64-encoded and line-wrapped to remain inside [MAIL] limits. base64 encoding is defined in [MIME]. o DKIM-Canonicalized-Header" contains the canonicalized message header block of a message which failed DKIM verification, base64- encoded and line-wrapped to remain inside [MAIL] limits. This filed SHOULD be included for DKIM reports. Shafranovich, et al. Expires April 22, 2010 [Page 8] Internet-Draft Format for Feedback Reports October 2009 o "DKIM-Domain" contains the domain whose private key was used to sign a message, taken from the signature's "d=" tag. o "DKIM-Identity" contains the signing agent's identity, taken from the signature's "i=" tag. o "DKIM-Selector" contains the selector referenced by a DKIM signature, taken from the signature's "s=" tag. 3.3. Optional Fields Appearing Multiple Times The following set of header fields are OPTIONAL and MAY appear more than once: o "Authentication-Results" indicates the result of one or more authentication checks run by the report generator. The format of this field is is defined in [AUTH-RESULTS]. Report receivers should note that this field only indicates an assertion made by the report generator. o "Original-Rcpt-To" includes a copy of the email address used in the RCPT TO portion of the original [SMTP] transaction. The format of this field is defined in section 4.1.1.3 of that memo. This field SHOULD be repeated for every SMTP recipient seen by the report generator. o "Removal-Recipient" indicates the email address to be removed from the mailing list (MUST NOT be used with report types other than "opt-out"). The format of this field is defined in section 3.4.1 of [MAIL]. o "Reported-Domain" includes a domain name that the report generator believes to be relevant to the report, e.g. the domain whose apparent actions provoked the generation of the report. Domain format is defined in section 2.3.1 of [DNS]. o "Reported-URI" indicates a URI that the report generator believes to be relevant to the report, e.g. a URI to which the report recipient can go for further details. URI format is defined in [URI]. 3.4. Formal Definition The formal definition of the contents of a "message/feedback-report" media type using [ABNF] is as follows: feedback-report = *( feedback-type / user-agent / version ) [ dkim-failure ] Shafranovich, et al. Expires April 22, 2010 [Page 9] Internet-Draft Format for Feedback Reports October 2009 opt-fields-once dkim-fields-once *( opt-fields-many ) feedback-type = "Feedback-Type:" [CFWS] token [CFWS] CRLF ; the "token" must be a registered feedback type as ; described elsewhere in this document user-agent = "User-Agent:" [CFWS] product [CFWS] CRLF version = "Version:" [CFWS] token [CFWS] CRLF ; as described above dkim-failure = "DKIM-Failure:" [CFWS] token [CFWS] CRLF ; the "token" must be a registered DKIM failure type ; as described elsewhere in this document opt-fields-once = [ arrival-date ] [ dkim-failure ] [ incidents ] [ original-envelope-id ] [ original-mail-from ] [ reporting-mta ] [ source-ip ] arrival-date = "Arrival-Date:" [CFWS] date-time [CFWS] CRLF incidents = "Incidents:" [CFWS] 1*DIGIT [CFWS] CRLF original-envelope-id = "Original-Envelope-Id:" [CFWS] envelope-id [CFWS] CRLF original-mail-from = "Original-Mail-From:" [CFWS] reverse-path [CFWS] CRLF reporting-mta = "Reporting-MTA:" [CFWS] mta-name [CFWS] CRLF source-ip = "Source-IP:" [CFWS] ( IPv4-address-literal / IPv6-address-literal ) [CFWS] CRLF dkim-fields-once = [ dkim-canon-body ] [ dkim-canon-header ] [ dkim-domain ] [ dkim-identity ] [ dkim-selector ] dkim-canon-body = "DKIM-Canonicalized-Body:" [CFWS] Shafranovich, et al. Expires April 22, 2010 [Page 10] Internet-Draft Format for Feedback Reports October 2009 base64string [CFWS] CRLF dkim-canon-header = "DKIM-Canonicalized-Header:" [CFWS] base64string [CFWS] CRLF dkim-domain = "DKIM-Domain:" [CFWS] domain-name [CFWS] CRLF dkim-identity = "DKIM-Domain:" [CFWS] [ local-part ] "@" domain-name [CFWS] CRLF dkim-selector = "DKIM-Selector:" [CFWS] selector [CFWS] CRLF opt-fields-many = [ authres-header ] [ original-rcpt-to ] [ removal-recipient ] [ reported-domain ] [ reported-uri ] original-rcpt-to = "Original-Rcpt-To:" [CFWS] forward-path [CFWS] CRLF removal-recipient = "Removal-Recipient:" [CFWS] mailbox [CFWS] CRLF reported-domain = "Reported-Domain:" [CFWS] domain-name [CFWS] CRLF reported-uri = "Reported-Domain:" [CFWS] URI [CFWS] CRLF A set of fields satisfying this ABNF may appear in the transmitted message in any order. "CRLF" is imported from [ABNF]. "token" is imported from [MIME]. "product" is imported from [HTTP]. "mailbox", "CFWS" and "date-time" are imported from [MAIL]. "envelope-id" and "mta-name" are imported from [DSN]. "reverse-path", "forward-path", "local-part", "IPv4-address-literal" and "IPv6-address-literal" are imported from [SMTP]. "base64string", "domain-name" and "selector" are imported from [DKIM]. Furthermore, a "base64string" SHOULD be line-wrapped as described in section 6.8 of [MIME]. Shafranovich, et al. Expires April 22, 2010 [Page 11] Internet-Draft Format for Feedback Reports October 2009 "URI" is imported from [URI]. "authres-header" is imported from [AUTH-RESULTS]. Shafranovich, et al. Expires April 22, 2010 [Page 12] Internet-Draft Format for Feedback Reports October 2009 4. Extensibility Like many other formats and protocols, this format may need to be extended over time to fit the ever changing landscape of the Internet. Therefore, extensibility is provided via two IANA registries: one for feedback types and a second for report header fields. The feedback type registry is to be used in conjunction with the "Feedback-Type" field above. The header name registry is intended for registration of new meta-data fields to be used in the machine readable portion (part 2) of this format. Please note that version numbers do not change with new field registrations unless a new specification of this format is published. Also note that all new field registrations may only be registered as OPTIONAL fields. Any new required fields REQUIRE a new version of this specification to be published. In order to encourage extensibility and interoperability of this format, implementors MUST ignore any fields they do not support. Shafranovich, et al. Expires April 22, 2010 [Page 13] Internet-Draft Format for Feedback Reports October 2009 5. IANA Considerations IANA is requested to register a new [MIME] type and create three new registries, as described below. 5.1. MIME Type Registration of 'message/feedback-report' This section provides the media type registration application from [MIME-REG] for processing by IANA: To: ietf-types@iana.org Subject: Registration of media type message/feedback-report Type name: message Subtype name: feedback-report Required parameters: none Optional parameters: none Encoding considerations: "7bit" encoding is sufficient and MUST be used to maintain readability when viewed by non-MIME mail readers. Security considerations: See the Security Considerations section of [this document]. Interoperability considerations: Implementors MUST ignore any fields they do not support. Published specification: [this document] Applications which use this media type: Abuse helpdesk software for ISPs, mail service bureaus, mail certifiers, and similar organizations Additional information: none Person and email address to contact for further information: Yakov Shafranovich Murray S. Kucherawy Shafranovich, et al. Expires April 22, 2010 [Page 14] Internet-Draft Format for Feedback Reports October 2009 Intended usage: COMMON Author: Yakov Shafranovich John Levine Murray S. Kucherawy Change controller: IESG 5.2. Feedback Report Header Fields IANA is requested to create the "Feedback Report Header Fields" registry. This registry will contain header fields for use in feedback reports, defined by this memo. New registrations to this registry MUST have approval by a Designated Expert in accordance with the Expert Review guidelines as described in [IANA-CONSIDERATIONS]. The expert should be appointed by the Area Director for the Applications Area. Any new field registered is considered OPTIONAL by this specification unless a new version of this memo is published. New registrations MUST contain the following information: 1. Name of the field being registered 2. Short description of the field 3. Whether the field can appear more than once 4. To which feedback type(s) this field applies (or "any") 5. The document in which the specification of the field is published The initial registry should contain these values: Field Name: Arrival-Date Description: date/time the original message was received Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Shafranovich, et al. Expires April 22, 2010 [Page 15] Internet-Draft Format for Feedback Reports October 2009 Field Name: Authentication-Results Description: results of authentication check(s) Multiple Appearances: Yes Related "Feedback-Type": any Published in: [this document] Field Name: DKIM-Canonicalized-Body Description: Canonicalized body, per DKIM, base64-encoded Multiple Appearances: No Related "Feedback-Type": dkim Published in: [this document] Field Name: DKIM-Canonicalized-Header Description: Canonicalized header blcok, per DKIM, base64-encoded Multiple Appearances: No Related "Feedback-Type": dkim Published in: [this document] Field Name: DKIM-Domain Description: selector from DKIM signature ("d=" signature tag value) Multiple Appearances: No Related "Feedback-Type": dkim Published in: [this document] Field Name: DKIM-Failure Description: registered DKIM failure type Multiple Appearances: No Related "Feedback-Type": dkim Published in: [this document] Field Name: DKIM-Identity Description: DKIM signing identity ("i=" signature tag value) Multiple Appearances: No Related "Feedback-Type": dkim Published in: [this document] Field Name: DKIM-Selector Description: selector from DKIM signature ("s=" signature tag value) Multiple Appearances: No Related "Feedback-Type": dkim Shafranovich, et al. Expires April 22, 2010 [Page 16] Internet-Draft Format for Feedback Reports October 2009 Published in: [this document] Field Name: Feedback-Type Description: registered feedback report type Multiple Appearances: No Related "Feedback-Type": N/A Published in: [this document] Field Name: Original-Mail-From Description: email address used in the MAIL FROM portion of the original SMTP transaction Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Field Name: Original-Rcpt-To Description: email address used in the RCPT TO portion of the original SMTP transaction Multiple Appearances: Yes Related "Feedback-Type": any Published in: [this document] Field Name: Received-Date Description: date/time the original message was received (historic; deprecated) Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Field Name: Removal-Recipient Description: email address to be removed from the mailing list Multiple Appearances: Yes Related "Feedback-Type": opt-out Published in: [this document] Field Name: Reported-Domain Description: relevant domain name Multiple Appearances: Yes Related "Feedback-Type": any Published in: [this document] Shafranovich, et al. Expires April 22, 2010 [Page 17] Internet-Draft Format for Feedback Reports October 2009 Field Name: Reported-URI Description: relevant URI Multiple Appearances: Yes Related "Feedback-Type": any Published in: [this document] Field Name: Reporting-MTA Description: MTA generating this report Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Field Name: Source-IP Description: IPv4 or IPv6 address from which the original message was received Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Field Name: User-Agent Description: name and version of the program generating the report Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] Field Name: Version Description: version of specification used Multiple Appearances: No Related "Feedback-Type": any Published in: [this document] 5.3. Feedback Report Type Values IANA is requested to create the "Feedback Report Type Values" registry. This registry will contain feedback types for use in feedback reports, defined by this memo. New registrations to this registry MUST have approval by a Designated Expert in accordance with the Expert Review guidelines as described in [IANA-CONSIDERATIONS]. The expert should be appointed by the Area Director for the Applications Area. Any new field registered is considered OPTIONAL by this specification unless a new version of this memo is published. Shafranovich, et al. Expires April 22, 2010 [Page 18] Internet-Draft Format for Feedback Reports October 2009 New registrations MUST contain the following information: 1. Name of the feedback type being registered 2. Short description of the feedback type 3. The document in which the specification of the field is published The initial registry should contain these values: Feedback Type Name: abuse Description: spam or some kind of email abuse Published in: [this document] Feedback Type Name: dkim Description: a DKIM signature verification or policy violation error Published in: [this document] Feedback Type Name: fraud Description: indicates some kind of fraud or phishing activity Published in: [this document] Feedback Type Name: miscategorized Description: indicates that the content categorization applied in connection with a certification or reputation system was incorrect Published in: [this document] Feedback Type Name: not-spam Description: indicates that a message that was tagged or categorized as spam (such as by an ISP) is not spam Published in: [this document] Feedback Type Name: opt-out Description: a request to opt out from mailings from this provider Published in: [this document] Feedback Type Name: other Description: any other feedback that does not fit into other registered types Shafranovich, et al. Expires April 22, 2010 [Page 19] Internet-Draft Format for Feedback Reports October 2009 Published in: [this document] Feedback Type Name: virus Description: report of a virus found in the originating message Published in: [this document] 5.4. Feedback Report DKIM Failure Values IANA is requested to create the "Feedback Report Header Fields" registry. This registry will contain header fields for use in feedback reports, defined by this memo. New registrations to this registry MUST have approval by a Designated Expert in accordance with the Expert Review guidelines as described in [IANA-CONSIDERATIONS]. The expert should be appointed by the Area Director for the Applications Area. Any new field registered is considered OPTIONAL by this specification unless a new version of this memo is published. New registrations MUST contain the following information: 1. Name of the DKIM failure type being registered 2. Short description of the failure type 3. The document in which the specification of the field is published The initial registry should contain these values: DKIM Failure Type: bodyhash Description: The body hash in the signature and the body hash computed by the verifier did not match. Published in: [this document] DKIM Failure Type: granularity Description: The key referenced by the signature on the message was not authorized for use by the sending user. Published in: [this document] DKIM Failure Type: other Description: The signature verification process failed for a reason not enumerated by some other registered DKIM failure type. Published in: [this document] Shafranovich, et al. Expires April 22, 2010 [Page 20] Internet-Draft Format for Feedback Reports October 2009 DKIM Failure Type: policy Description: The DKIM Author Domain Signing Practises (ADSP) evaluation failed. Published in: [this document] DKIM Failure Type: revoked Description: The key referenced by the signature on the message has been revoked. Published in: [this document] DKIM Failure Type: signature Description: The signature on the message did not successfully verify against the header hash and public key. Published in: [this document] DKIM Failure Type: syntax Description: The key referenced by the signature on the message, or the signature itself, contained a syntax error. Published in: [this document] Shafranovich, et al. Expires April 22, 2010 [Page 21] Internet-Draft Format for Feedback Reports October 2009 6. Security Considerations The following security considerations apply when generating or processing a feedback report: 6.1. Inherited from RFC3462 All of the Security Considerations from [REPORT] are inherited here. 6.2. Interpretation This specification describes a report format. This memo makes no normative assertions of any kind about actions to be taken by recipients of these reports. Actions taken by recipients are done entirely at their own discretion. There will be some desire to perform some actions in an automated fashion in order to enact timely responses to common feedback reports. Caution must be taken, however, as there is no substantial security around the content of these reports. An attacker could craft a report meant to generate undesirable actions on the part of a report recipient. It is recommended that ARF reports be vetted using common message authentication schemes such as [DKIM], [SPF] or [SENDERID] to confirm that they represent a valid message from the purported sender of the report prior to the undertaking of any kind of automated action in response to receipt of the report. 6.3. Envelope Sender Selection When generating an ARF message, it is necessary to construct the message so as to avoid amplification or backscatter attacks, deliberate or otherwise. Thus, per Section 2 of [DSN], the envelope sender address of the ARF message should be chosen to ensure that no delivery status reports will be issued in response to the ARF message itself, and must be chosen so that these reports will not generate mail loops. Whenever an SMTP transaction is used to send an ARF message, the MAIL FROM command must use a NULL return address, i.e. "MAIL FROM:<>". 6.4. Attacks Against Authentication Methods If an attack becomes known against an authentication method, clearly then the agent verifying that method can be fooled into thinking an inauthentic message is authentic, and thus the value of this header field can be misleading. It follows that any attack against the authentication methods supported by this document (and later Shafranovich, et al. Expires April 22, 2010 [Page 22] Internet-Draft Format for Feedback Reports October 2009 amendments to it) is also a security consideration here. 6.5. Intentionally Malformed Reports It is possible for an attacker to generate an ARF message field which is extraordinarily large or otherwise malformed in an attempt to discover or exploit weaknesses in recipient parsing code. Implementors must thoroughly verify all such messages and be robust against intentionally as well as unintentionally malformed messages. Shafranovich, et al. Expires April 22, 2010 [Page 23] Internet-Draft Format for Feedback Reports October 2009 7. References 7.1. Normative References [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 5234, January 2008. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [MAIL] Resnick, P., "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. [MIME-REG] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", RFC 4288, December 2005. [MIME-TYPES] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [REPORT] Vaudreuil, G., "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 3462, January 2003. 7.2. Informative References [ASRG-ABUSE] Anti-Spam Research Group (ASRG) of the Internet Research Task Force (IRTF), "Abuse Reporting Standards Subgroup oof the ASRG", May 2005. [AUTH-RESULTS] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 5451, April 2009. [DKIM] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, J., and M. Thomas, "DomainKeys Identified Mail (DKIM) Signatures", RFC 4871, May 2007. [DNS] Mockapetris, P., "Domain Names -- Implementation and Specification", RFC 1035, November 1987. Shafranovich, et al. Expires April 22, 2010 [Page 24] Internet-Draft Format for Feedback Reports October 2009 [DSN] Moore, K. and G. Vaudreuil, "An Extensible Message Format for Delivery Status Notifications", RFC 3464, January 2003. [HTTP] 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. [I-D.DRAFT-CROCKER-EMAIL-ARCH] Crocker, D., "Internet Mail Architecture", draft-crocker-email-arch (work in progress), May 2007. [IANA-CONSIDERATIONS] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, May 2008. [SENDERID] Lyon, J. and M. Wong, "Sender ID: Authenticating E-Mail", RFC 4406, April 2006. [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. [STRADS-BCP] Crissman, G., "Proposed Spam Reporting BCP Document", May 2005. [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", RFC 3986, January 2005. Shafranovich, et al. Expires April 22, 2010 [Page 25] Internet-Draft Format for Feedback Reports October 2009 Appendix A. Acknowledgements The authors would like to thank many of the members of the email community who provided helpful comments and suggestions for this document including many of the participants in ASRG, IETF and MAAWG activities, and all of the members of the abuse-feedback-report public mailing list. Shafranovich, et al. Expires April 22, 2010 [Page 26] Internet-Draft Format for Feedback Reports October 2009 Appendix B. Sample Feedback Reports This section presents some examples of the use of this message format to report feedback about an arriving message. B.1. Simple Report for Email Abuse without Optional Headers Simple report: Shafranovich, et al. Expires April 22, 2010 [Page 27] Internet-Draft Format for Feedback Reports October 2009 From: Date: Thu, 8 Mar 2005 17:40:36 EDT Subject: FW: Earn money To: MIME-Version: 1.0 Content-Type: multipart/report; report-type=feedback-report; boundary="part1_13d.2e68ed54_boundary" --part1_13d.2e68ed54_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit This is an email abuse report for an email message received from IP 192.0.2.1 on Thu, 8 Mar 2005 14:00:00 EDT. For more information about this format please see http://www.mipassoc.org/arf/. --part1_13d.2e68ed54_boundary Content-Type: message/feedback-report Feedback-Type: abuse User-Agent: SomeGenerator/1.0 Version: 0.1 --part1_13d.2e68ed54_boundary Content-Type: message/rfc822 Content-Disposition: inline From: Received: from mailserver.example.net (mailserver.example.net [192.0.2.1]) by example.com with ESMTP id M63d4137594e46; Thu, 08 Mar 2005 14:00:00 -0400 To: Subject: Earn money MIME-Version: 1.0 Content-type: text/plain Message-ID: 8787KJKJ3K4J3K4J3K4J3.mail@example.net Date: Thu, 02 Sep 2004 12:31:03 -0500 Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam --part1_13d.2e68ed54_boundary-- Example 1: Required fields only Illustration of a feedback report generated according to this Shafranovich, et al. Expires April 22, 2010 [Page 28] Internet-Draft Format for Feedback Reports October 2009 specification. Only the required fields are used. B.2. Opt-Out Report without Message Body A sample opt-out report From: Date: Thu, 8 Mar 2005 17:40:36 EDT Subject: FW: Earn money To: MIME-Version: 1.0 Content-Type: multipart/report; report-type=feedback-report; boundary="part1_13d.2e68ed54_boundary" --part1_13d.2e68ed54_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit This is an opt-out report for an email message received from IP 192.0.2.1 on Thu, 8 Mar 2005 14:00:00 EDT. For more information about this format please see http://www.mipassoc.org/arf/. --part1_13d.2e68ed54_boundary Content-Type: message/feedback-report Feedback-Type: opt-out User-Agent: SomeGenerator/1.0 Version: 0.1 Removal-Recipient: user@example.com --part1_13d.2e68ed54_boundary Content-Type: text/rfc822-header From: Received: from mailserver.example.net (mailserver.example.net [192.0.2.1]) by example.com with ESMTP id M63d4137594e46; Thu, 08 Mar 2005 14:00:00 -0400 To: Subject: Earn money MIME-Version: 1.0 Content-type: text/plain Message-ID: 8787KJKJ3K4J3K4J3K4J3.mail@example.net Date: Thu, 02 Sep 2004 12:31:03 -0500 --part1_13d.2e68ed54_boundary-- Example 2: An opt-out feedback report, which indicates the address of a user who wishes to opt out of a mailing list Shafranovich, et al. Expires April 22, 2010 [Page 29] Internet-Draft Format for Feedback Reports October 2009 The report is generated as a result of a user indicating to its ISP that it does not wish to receive further messages of this kind. The report returned only the header block from the original message. The report's recipient receives the address of the requesting user and can use the header block and its own records to determine from which distribution list the requesting user should be removed. B.3. Full Report for Email Abuse with All Headers A full email abuse report: From: Date: Thu, 8 Mar 2005 17:40:36 EDT Subject: FW: Earn money To: MIME-Version: 1.0 Content-Type: multipart/report; report-type=feedback-report; boundary="part1_13d.2e68ed54_boundary" --part1_13d.2e68ed54_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit This is an email abuse report for an email message received from IP 192.0.2.1 on Thu, 8 Mar 2005 14:00:00 EDT. For more information about this format please see http://www.mipassoc.org/arf/. --part1_13d.2e68ed54_boundary Content-Type: message/feedback-report Feedback-Type: abuse User-Agent: SomeGenerator/1.0 Version: 0.1 Original-Mail-From: Original-Rcpt-To: Received-Date: Thu, 8 Mar 2005 14:00:00 EDT Source-IP: 192.0.2.1 Authentication-Results: mail.example.com smtp.mail=somespammer@example.com; spf=fail Reported-Domain: example.net Reported-Uri: http://example.net/earn_money.html Reported-Uri: mailto:user@example.com Removal-Recipient: user@example.com --part1_13d.2e68ed54_boundary Content-Type: message/rfc822 Content-Disposition: inline Shafranovich, et al. Expires April 22, 2010 [Page 30] Internet-Draft Format for Feedback Reports October 2009 From: Received: from mailserver.example.net (mailserver.example.net [192.0.2.1]) by example.com with ESMTP id M63d4137594e46; Thu, 08 Mar 2005 14:00:00 -0400 To: Subject: Earn money MIME-Version: 1.0 Content-type: text/plain Message-ID: 8787KJKJ3K4J3K4J3K4J3.mail@example.net Date: Thu, 02 Sep 2004 12:31:03 -0500 Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam Spam --part1_13d.2e68ed54_boundary-- Example 3: Generic abuse report with maximum returned information A contrived example in which the report generator has returned all possible information about an abuse incident. B.4. Sample DKIM Failure Report [TBD] Shafranovich, et al. Expires April 22, 2010 [Page 31] Internet-Draft Format for Feedback Reports October 2009 Appendix C. Public Discussion, History and Support [REMOVE BEFORE PUBLICATION] Public discussion of this proposed specification is handled via the abuse-feedback-report@mipassoc.org mailing list. The list is open. Access to subscription forms and to list archives can be found at http://mipassoc.org/mailman/listinfo/abuse-feedback-report. Active participation has included such sectors as messaging software vendors, messaging service providers, messaging consultants, anti- spam vendors, large Internet service providers, etc. Copies of this and earlier versions including multiple formats can be found at . A public website regarding this draft and related efforts is located at . (impetus for the work should be discussed here) (MAAWG activity should be discussed here) Several companies have already adopted use of this proposal, including large-scale e-mail hosting providers and Internet service providers. For a list of these, see the PROTO document supporting this draft. Shafranovich, et al. Expires April 22, 2010 [Page 32] Internet-Draft Format for Feedback Reports October 2009 Appendix D. Document History Changes from draft-shafranovich-feedback-report-01-pre1 to draft-shafranovich-feedback-report-01: o Added an "Outstanding Issues" section. o Minor spelling mistakes and clarifications. o Added links to previous work and more examples. o Added three new types: "fraud" for phishing, "opt-out-list" for a single list opt out, and "other" as a catch-all. Changes from draft-shafranovich-feedback-report-00 to draft-shafranovich-feedback-report-01-pre1: o Changed the introduction section to clarify specific points that are out of scope for this document. o Added pointers to a public mailing list for discussion and public web page. o Clarified the intent section and added some extra points to it. o Made it clear that the requirements section is not the one defining the standard. o Clarified the main format section to make all three parts mandatory. o Changed section 4f regarding subject lines to mandate that subject lines should be left intact. Removed the convention for subject lines that was defined in the previous version. o Added text to the the machine readable section clarifying its intent. Also added RFC2119 references, reorganized fields, indicated whether specific header fields can appear more than once and provided references as to how they should be formatted. o Removed "Original-Message-ID", "Authenticated-Domain" and "Authenticated-Domain-Method" from the draft including related IANA registries. Added "Version", "User-Agent", Original-Mail- From", "Original-Rcpt-To", "Reported-URI", "Reported-Domain" and "Authentication-Results". o Example has been updated to reflect new fields. Shafranovich, et al. Expires April 22, 2010 [Page 33] Internet-Draft Format for Feedback Reports October 2009 o Added a new section on extensibility and changed the IANA section to reflect that. Changes from draft-shafranovich-abuse-report-00 to draft-shafranovich-feedback-report-00: o Name of the format and report changed to 'feedback-report' o Minor spelling corrections o Added authentication headers and registry o Added feedback-type header and registry Changes from draft-shafranovich-feedback-report-00 to draft-shafranovich-feedback-report-01: o None significant (just a freshening) Changes from draft-shafranovich-feedback-report-01 to draft-shafranovich-feedback-report-02: o Much editorial cleanup o Added John Levine and Paul Hoffman as co-authors o Made the line lengths in Appendix A appropriate for RFCs o Switched to symbolic names for references o Reduced duplication of reference calls o Removed text that specified the type of RFC and approval type that is expected o Removed the requirement for an RFC to update the IANA registries; both are now designated expert approval only o Added two new categories to the initial values for the "Feedback- Type" registry: "miscategorized" and "not-spam" Changes from draft-shafranovich-feedback-report-02 to draft-shafranovich-feedback-report-03: o Added a bit to the Security Considerations section o Updated obsolete references Shafranovich, et al. Expires April 22, 2010 [Page 34] Internet-Draft Format for Feedback Reports October 2009 o Resolved all items in the outstanding issues list and therefore removed it Changes from draft-shafranovich-feedback-report-03 to draft-shafranovich-feedback-report-04: o Added Murray Kucherawy as co-author o Added support for DKIM reporting o Cleaned up XML a lot Changes from draft-shafranovich-feedback-report-04 to draft-shafranovich-feedback-report-05: o Add "Incidents" header o RFC3464 replaces RFC1894 o RFC5226 replaces RFC2434 Changes from draft-shafranovich-feedback-report-05 to draft-shafranovich-feedback-report-06: o Remove Paul Hoffman as co-author, per his request o Add ABNF section o Move MIME registration stuff from the earlier sections to the IANA Considerations section o Some other minor re-organization o Add more stuff to Security Considerations o Add more project history o Overhaul the XML o Add and update several references; use symbolic references instead of numbered ones o Use RFC3330 "TEST-NET" addresses in examples o Fix some typos Changes from draft-shafranovich-feedback-report-06 to draft-shafranovich-feedback-report-07: Shafranovich, et al. Expires April 22, 2010 [Page 35] Internet-Draft Format for Feedback Reports October 2009 o I-D.DRAFT-KUCHERAWY-SENDER-AUTH-HEADER published as RFC5451 Changes from draft-shafranovich-feedback-report-07 to draft-shafranovich-feedback-report-08: o None. Still to be done: o Add a DKIM example o Add explicit extension field and type support Shafranovich, et al. Expires April 22, 2010 [Page 36] Internet-Draft Format for Feedback Reports October 2009 Authors' Addresses Yakov Shafranovich ShafTek Enterprises 4014 Labyrinth Rd. Baltimore, MD 21215 Email: ietf@shaftek.org URI: http://www.shaftek.org John Levine Domain Assurance Council PO Box 727 Trumansburg, NY 14886 Phone: +1 831 480 2300 Email: john.levine@domain-assurance.org URI: http://www.domain-assurance.org Murray S. Kucherawy Cloudmark 128 King St., 2nd Floor San Francisco, CA 94107 US Phone: +1 415 946 3800 Email: msk@cloudmark.com Shafranovich, et al. Expires April 22, 2010 [Page 37]