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Versions: (draft-kucherawy-dkim-reporting) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 6651

MARF Working Group                                          M. Kucherawy
Internet-Draft                                                 Cloudmark
Intended status: Standards Track                        January 25, 2012
Expires: July 28, 2012


                Extensions to DKIM for Failure Reporting
                   draft-ietf-marf-dkim-reporting-06

Abstract

   This memo presents extensions to the DomainKeys Identified Mail
   (DKIM) specification to allow for detailed reporting of message
   authentication failures in an on-demand fashion.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 28, 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Keywords . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Imported Definitions . . . . . . . . . . . . . . . . . . .  4
   3.  Optional Reporting for DKIM  . . . . . . . . . . . . . . . . .  5
     3.1.  Extension DKIM Signature Tag . . . . . . . . . . . . . . .  5
     3.2.  DKIM Reporting TXT Record  . . . . . . . . . . . . . . . .  5
     3.3.  DKIM Reporting Algorithm . . . . . . . . . . . . . . . . .  7
   4.  Optional Reporting Address for DKIM-ADSP . . . . . . . . . . .  9
   5.  Requested Reports  . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Requested Reports for DKIM Failures  . . . . . . . . . . . 11
     5.2.  Requested Reports for DKIM ADSP Failures . . . . . . . . . 11
   6.  Report Generation  . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Report Format  . . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  Envelope Sender Selection  . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  DKIM Signature Tag Registration  . . . . . . . . . . . . . 13
     7.2.  DKIM ADSP Tag Registration . . . . . . . . . . . . . . . . 13
     7.3.  DKIM Reporting Tag Registry  . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     8.1.  Inherited Considerations . . . . . . . . . . . . . . . . . 15
     8.2.  Deliberate Misuse  . . . . . . . . . . . . . . . . . . . . 15
     8.3.  Forgeries  . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.4.  Amplification Attacks  . . . . . . . . . . . . . . . . . . 15
     8.5.  Automatic Generation . . . . . . . . . . . . . . . . . . . 15
     8.6.  Reporting Multiple Incidents . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 19
   Appendix B.  Examples  . . . . . . . . . . . . . . . . . . . . . . 20
     B.1.  Example Use of DKIM Signature Extension Tags . . . . . . . 20
     B.2.  Example Use of DKIM ADSP Extension Tags  . . . . . . . . . 20
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22















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1.  Introduction

   [DKIM] introduced a mechanism for message signing and authentication.
   It uses digital signing to associate a domain name with a message in
   a reliable (i.e. not forgeable) manner.  The output is a verified
   domain name that can then be subjected to some sort of evaluation
   process (e.g., advertised sender policy, comparison to a known-good
   list, submission to a reputation service, etc.).

   Deployers of message authentication technologies are increasingly
   seeking visibility into DKIM verification failures and conformance
   failures involving the published signing practices (e.g., [ADSP]) of
   an Administrative Management Domain (ADMD; see [EMAIL-ARCH]).

   This document extends [DKIM] and [ADSP] to add an optional reporting
   address and some reporting parameters.



































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2.  Definitions

2.1.  Keywords

   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 imported from [MIME].

   Numerous DKIM-specific terms used here are defined in [DKIM].  The
   definition of the ABNF token "domain-name" can also be found there.





































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3.  Optional Reporting for DKIM

   A domain name owner employing [DKIM] for email signing and
   authentication might want to know when signatures in use by specific
   keys are not successfully verifying.  Currently there is no such
   mechanism defined.

   This document adds optional "tags" (as defined in [DKIM]) to the
   DKIM-Signature header field and the DKIM key record in the DNS, using
   the formats defined in that specification.

3.1.  Extension DKIM Signature Tag

   The following tag is added to DKIM-Signature header fields when a
   Signer wishes to request that reports of failed verifications be
   generated by a Verifier:

   rd=  Reporting Domain (plain-text; OPTIONAL; no default).  The value
      MUST be a string containing a DNS domain name.  This value will be
      used by the Verifier to confirm that failed verification reports
      are desired and collect report generation parameters.  A complete
      description and illustration of how this is applied can be found
      in Section 3.3.

   ABNF:

       sig-rd-tag = %x72.64 *WSP "=" *WSP domain-name

3.2.  DKIM Reporting TXT Record

   When a Signer wishes to advertise that it wants to receive failed
   verification reports, it also places in the DNS a TXT resource record
   (RR) whose content follows the same general syntax as DKIM key
   records, as defined in Section 3.6.1 of [DKIM], in that it is made up
   of a sequence of tag-value objects.  In this case, the tags and
   values comprise the parameters to be used when generating the
   reports.  The Verifier (if it supports this extension) will request
   the content of this record when it sees an "rd=" tag in a DKIM-
   Signature header field.

   The reassembly rules of Section 3.6.2.2 of [DKIM] also apply here if
   the reporting TXT record consists of several string fragments.

   Any tag found in the content of this record that is not registered
   with IANA as described in Section 7.3 MUST be ignored.

   The initial list of tags supported for the reporting TXT record is as
   follows:



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   ra=  Reporting Address (plain-text; REQUIRED).  A dkim-quoted-
      printable string (see Section 2.11 of [DKIM]) containing the
      local-part of an email address to which a report SHOULD be sent
      when mail fails DKIM verification for one of the reasons
      enumerated below.  The value MUST be interpreted as a local-part
      only.  To construct the actual address to which the report is
      sent, the verifier simply appends to this value an "@" followed by
      the domain name found in the "rd=" tag of the DKIM-Signature
      header field.  Therefore, an ADMD making use of this specification
      MUST ensure that an email address thus constructed can receive
      reports generated as described in Section 6.  ABNF:

       rep-ra-tag = %x72.61 *WSP "=" *WSP qp-section

   rp=  Requested Report Percentage (plain-text; OPTIONAL; default is
      "100").  The value is an integer value from 0 to 100 inclusive
      that indicates what percentage of incidents of signature
      authentication 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.  Report
      generators MAY make use of the "Incidents:" field in [ARF] to
      indicate that there are more reportable incidents than there are
      reports.  ABNF:

       rep-rp-tag = %x72.70 *WSP "=" *WSP 1*3DIGIT

   rr=  Requested Reports (plain-text; OPTIONAL; default is "all").  The
      value MUST be a colon-separated list of tokens representing those
      conditions under which a report is desired.  See Section 5.1 for a
      list of valid tags.  ABNF:

       rep-rr-type = ( "all" / "s" / "v" / "x" )
       rep-rr-tag = %x72.72 *WSP "=" *WSP rep-rr-type
                    *WSP 0* ( ":" *WSP rep-rr-type )

   rs=  Requested SMTP Error String (text; OPTIONAL; no default).  The
      value is a dkim-quoted-printable string that the publishing ADMD
      requests be included in [SMTP] error strings if messages are
      rejected during the delivery SMTP session.  ABNF:

       rep-rs-tag = %x72.73 *WSP "=" qp-section

   In the absence of an "ra=" tag, all other tags listed above MUST be
   ignored.  In other words, an implementation MUST NOT have a default
   value for the "ra=" tag.






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3.3.  DKIM Reporting Algorithm

   The following algorithm, or one semantically equivalent to it, MUST
   be applied when an implementation is equipped to generate reports in
   compliance with this specification and its evaluation of the DKIM-
   Signature header field (see [DKIM]) on a message fails for some
   reason.  Note that this processing is done as a reporting extension
   only; the outcome of the specified DKIM evaluation is otherwise
   unaffected.

   1.   If the DKIM-Signature field did not contain an "rd=" tag,
        terminate.

   2.   Issue a [DNS] TXT query to the name that results from appending
        the value of the "rd=" tag to the string "_report._domainkey".
        For example, if a DKIM-Signature header field contains
        "example.com", issue a DNS TXT query to
        "_report._domainkey.example.com".

   3.   If the DNS query returns anything other than a success status
        code (0), also known as NOERROR, the implementation MAY log this
        locally; in either case, terminate.

   4.   If the resultant TXT is in several string fragments, reassemble
        it as described in Section 3.6.2.2 of [DKIM].

   5.   If the TXT content is syntactically invalid, the implementation
        MAY log this locally; in either case, terminate.

   6.   If the reason for the signature evaluation failure does not
        match one of the report requests found in the "rr=" tag (or its
        default value), terminate.

   7.   If a report percentage ("rp=") tag was present, select a random
        number between 0 and 99, inclusive; if the selected number is
        higher than the tag's value, terminate.

   8.   Determine the reporting address by extracting the value of the
        "ra=" tag and appending to it "@" followed by the domain name
        found in the "rd=" tag of the DKIM-Signature header field.

   9.   Construct and send a report in compliance with Section 6 of this
        memo that includes as its intended recipient the address
        constructed in the previous step.

   10.  If the [SMTP] session during which the DKIM signautre was
        evaluated is still active and the SMTP server has not already
        given its response to the DATA command that relayed the message,



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        and an "rs=" tag was present in the TXT record, the SMTP server
        SHOULD include the decoded string found in the "rs=" tag in its
        SMTP reply to the DATA command.

   This algorithm has the following advantages over previous
   implementations:

   a.  If the DKIM signature fails to verify, no additional DNS check is
       made to see if reporting is requested; the request is active in
       that it is included in the DKIM-Signature header field.
       (Previous implementations included the reporting address in the
       DKIM key record, which is not queried for certain failure cases.
       This meant, for full reporting, that the key record had to be
       retrieved even when it was not otherwise necessary.)

   b.  The request is confirmed by the presence of a corresponding TXT
       record in the DNS, since the Signer thus provides the parameters
       required to construct and send the report.  This means a
       malicious Signer cannot falsely assert that someone else wants
       failure reports.  It can cause additional DNS traffic against the
       domain listed in the "rd=" signature tag, but negative caching of
       the requested DNS record will help to mitigate this issue.

   c.  It is not possible for a Signer to direct reports to an email
       address outside of its own domain, preventing distributed email-
       based denial-of-service attacks.

























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4.  Optional Reporting Address for DKIM-ADSP

   There also exist cases in which a domain name owner employing [ADSP]
   for announcing signing practises with DKIM may want to know when
   messages are received without valid author domain signatures.
   Currently there is no such mechanism defined.

   This document adds the following optional "tags" (as defined in
   [ADSP]) to the DKIM ADSP records, using the form defined in that
   specification:

   ra=  Reporting Address (plain-text; OPTIONAL; no default).  The value
      MUST be a dkim-quoted-printable string containing the local-part
      of an email address to which a report SHOULD be sent when mail
      claiming to be from this domain failed the verification algorithm
      described in [ADSP], in particular because a message arrived
      without a signature that validates, which contradicts what the
      ADSP record claims.  The value MUST be interpreted as a local-part
      only.  To construct the actual address to which the report is
      sent, the verifier simply appends to this value an "@" followed by
      the domain whose policy was queried in order to evaluate the
      sender's ADSP, i.e., the one taken from the RFC5322.From domain of
      the message under evaluation.  Therefore, a signer making use of
      this extension tag MUST ensure that an email address thus
      constructed can receive reports generated as described in
      Section 6.  ABNF:

       adsp-ra-tag = %x72.61 *WSP "=" qp-section

   rp=  Requested Report Percentage (plain-text; OPTIONAL; default is
      "100").  The value is a single integer value from 0 to 100
      inclusive that indicates what percentage of incidents of ADSP
      evaluation failures, selected at random, should cause reports to
      be generated.  The report generator SHOULD NOT issue reports for
      more than the requested percentage of incidents.  Report
      generators MAY make use of the "Incidents:" field in [ARF] to
      indicate that there are more reportable incidents than there are
      reports.  ABNF:

       adsp-rp-tag = %x72.70 *WSP "=" *WSP 1*3DIGIT

   rr=  Requested Reports (plain-text; OPTIONAL; default is "all").  The
      value MUST be a colon-separated list of tokens representing those
      conditions under which a report is desired.  See Section 5.2 for a
      list of valid tags.  ABNF:

       adsp-rr-type = ( "all" / "s" / "u" )
       adsp-rr-tag = %x72.72 *WSP "=" *WSP adsp-rr-type



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                     *WSP 0* ( ":" *WSP adsp-rr-type )

   rs=  Requested SMTP Error String (plain-text; OPTIONAL; no default).
      The value is a string the signing domain requests be included in
      [SMTP] error strings when messages are rejected during a single
      SMTP session.  ABNF:

       adsp-rs-tag = %x72.73 *WSP "=" qp-section

   In the absence of an "r=" tag, all other tags listed above MUST be
   ignored.








































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5.  Requested Reports

   This memo also includes, as the "ro" tags defined above, the means by
   which the signer 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 these lists.

5.1.  Requested Reports for DKIM Failures

   The following report requests are defined for DKIM keys:

   all  All reports are requested.

   s  Reports are requested for signature or key syntax errors.

   v  Reports are requested for signature verification failures or body
      hash mismatches.

   x  Reports are requested for signatures rejected by the verifier
      because the expiration time has passed.

5.2.  Requested Reports for DKIM ADSP Failures

   The following report requests are defined for ADSP records:

   all  All reports are requested.

   s  Reports are requested for messages that have a valid [DKIM]
      signature but do not match the published [ADSP] policy.

   u  Reports are requested for messages that have no valid [DKIM]
      signature and do not match the published [ADSP] policy.


















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6.  Report Generation

   This section describes the process for generating and sending reports
   in accordance with the request of the signer and/or sender as
   described above.

6.1.  Report Format

   All reports generated as a result of requests contained in these
   extension parameters MUST be generated in compliance with [ARF] and
   its extension specific to this work, [I-D.MARF-AUTHFAILURE-REPORT].

6.2.  Envelope Sender Selection

   In the case of transmitted reports in the form of a new message
   (versus rejections during an [SMTP] session), it is necessary to
   construct the message so as to avoid amplification attacks,
   deliberate or otherwise.  The envelope sender address of the report
   needs to be chosen so that these reports will not generate mail
   loops.

   Similar to Section 2 of [DSN], the envelope sender address of the
   report SHOULD 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 MUST either use the NULL return address, i.e.,
   "MAIL FROM:<>", or one that will pass [SPF] MAIL FROM checks on
   receipt.  The HELO/EHLO command SHOULD also be selected so that it
   wil pass [SPF] HELO checks.





















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7.  IANA Considerations

   As required by [IANA-CONSIDERATIONS], this section contains registry
   information for the new [DKIM] signature tags, and the new [ADSP]
   tags.  It also creates a DKIM reporting tag registry.

7.1.  DKIM Signature Tag Registration

   IANA is requested to update the DKIM Signature Tag Specification
   Registry to include the following new items:

                 +------+-----------------+--------+
                 | TYPE | REFERENCE       | STATUS |
                 +------+-----------------+--------+
                 | rd   | (this document) | active |
                 +------+-----------------+--------+

7.2.  DKIM ADSP Tag Registration

   IANA is requested to update the DKIM ADSP Specification Tag Registry
   to include the following new items:

                 +------+-----------------+
                 | TYPE | REFERENCE       |
                 +------+-----------------+
                 | ra   | (this document) |
                 | rp   | (this document) |
                 | rr   | (this document) |
                 | rs   | (this document) |
                 +------+-----------------+

7.3.  DKIM Reporting Tag Registry

   IANA is requested to create a sub-registry of the DKIM Parameters
   registry called "DKIM Reporting Tags".  Additions to this registry
   follow the "Specification Required" rules, with the following columns
   required for all registrations:

   Type:  The name of the tag being used in reporting records

   Reference:  The document that specifies the tag being defined

   Status:  The status of the tag's current use, either "active"
      indicating active use, or "historic" indicating discontinued or
      deprecated use

   The initial registry entries are as follows:




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                 +------+-----------------+--------+
                 | TYPE | REFERENCE       | STATUS |
                 +------+-----------------+--------+
                 | ra   | (this document) | active |
                 | rp   | (this document) | active |
                 | rr   | (this document) | active |
                 | rs   | (this document) | active |
                 +------+-----------------+--------+











































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8.  Security Considerations

   Security issues with respect to these reports are similar to those
   found in [DSN].

8.1.  Inherited Considerations

   Implementers are advised to consider the Security Considerations
   sections of [DKIM] and [ADSP].

8.2.  Deliberate Misuse

   Some threats caused by deliberate misuse of this mechanism are
   discussed in Section 3.3.

8.3.  Forgeries

   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.

   Security threats related to forged reports include the sending of:

   a.  A falsified authentication failure notification when the message
       was in fact delivered to the indicated recipient;

   b.  Falsified signature information, such as selector, domain, etc.

   Perhaps the simplest means of mitigating this threat is to assert
   that these reports should themselves be signed with something like
   DKIM.  On the other hand, if there's a problem with the DKIM
   infrastructure at the verifier, signing DKIM failure reports may
   produce reports that aren't trusted or even accepted by their
   intended recipients.

8.4.  Amplification Attacks

   Failure to compile with the normative statements in Section 6.2 can
   lead to amplification denial-of-service attacks.  See that section
   for details.

8.5.  Automatic Generation

   The mechanisms described in this memo are primarily intended for use
   in generating reports to aid implementers of [DKIM] and [ADSP] and
   other related protocols in development and debugging.  Therefore,



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   they are not designed for prolonged forensic use.  However, such uses
   are possible by ADMDs that want to keep a close watch for fraud or
   infrastructure problems.

   Automatic generation of these reports by verifying agents can cause a
   denial-of-service attack when a large volume of email is sent that
   causes authentication failures for whatever reason.

   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 report
   generators only create these (or any) ARF reports after an out-of-
   band arrangement has been made between two parties.  This mechanism
   then becomes a way to adjust parameters of an authorized abuse report
   feedback loop that is configured and activated by private agreement
   rather than starting to send them automatically based solely on data
   found in the DKIM signatures, which could have been fraudulently
   inserted.

8.6.  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 innundated 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] provides a limited form of
   mitigation.  The host generating reports may elect to send reports
   only periodically, with each report representing a number of
   identical or near-identical incidents.  One might even do 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 for "near-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
   may 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.






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9.  References

9.1.  Normative References

   [ADSP]     Allman, E., Delany, M., Fenton, J., and J. Levine, "DKIM
              Sender Signing Practises", RFC 5617, August 2009.

   [ARF]      Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              August 2010.

   [DKIM]     Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
              "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376,
              September 2011.

   [DNS]      Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [EMAIL-ARCH]
              Crocker, D., "Internet Mail Architecture", RFC 5598,
              October 2008.

   [I-D.MARF-AUTHFAILURE-REPORT]
              Fontana, H., "Authentication Failure Reporting using the
              Abuse Report Format",
              I-D draft-ietf-marf-authfailure-report, January 2012.

   [IANA-CONSIDERATIONS]
              Alvestrand, H. and T. Narten, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226, May 2008.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [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.






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9.2.  Informative References

   [DSN]      Moore, K. and G. Vaudreuil, "An Extensible Message Format
              for Delivery Status Notifications", RFC 3464,
              January 2003.














































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Appendix A.  Acknowledgements

   The authors wish to acknowledge the following for their review and
   constructive criticism of this proposal: Steve Atkins, Monica Chew,
   Dave Crocker, Tim Draegen, Frank Ellermann, JD Falk, John Levine, and
   Scott Kitterman.













































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Appendix B.  Examples

   This section contains examples of the use of each of the extensions
   defined by this memo.

B.1.  Example Use of DKIM Signature Extension Tags

   A DKIM-Signature field including use of the extensions defined by
   this memo:

       DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;
               d=example.com; s=jan2012;
               r=dkim-errors; ro=v:x;
               h=from:to:subject:date:message-id;
               bh=YJAYwiNdc3wMh6TD8FjVhtmxaHYHo7Z/06kHQYvQ4tQ=;
               b=jHF3tpgqr6nH/icHKIqFK2IJPtCLF0CRJaz2Hj1Y8yNwTJ
                 IMYIZtLccho3ymGF2GYqvTl2nP/cn4dH+55rH5pqkWNnuJ
                 R9z54CFcanoKKcl9wOZzK9i5KxM0DTzfs0r8

   Example 1: DKIM-Signature field using these extensions

   This example DKIM-Signature field contains the following data in
   addition to the basic DKIM signature data:

   o  Reports about signature evaluation failures should be send to the
      address "dkim-errors" at the signer's domain;

   o  Only reports about signature verification failures and expired
      signatures should be generated.

B.2.  Example Use of DKIM ADSP Extension Tags

   A DKIM ADSP record including use of the extensions defined by this
   memo:

       dkim=all; r=dkim-adsp-errors; ro=u

   Example 2: DKIM ADSP record using these extensions

   This example ADSP record makes the following assertions:

   o  The sending domain (i.e. the one that is advertising this policy)
      signs all mail it sends;

   o  Reports about ADSP evaluation failures should be send to the
      address "dkim-adsp-errors" at the sender's domain;





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   o  Only reports about unsigned messages should be generated.


















































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Author's Address

   Murray S. Kucherawy
   Cloudmark
   128 King St., 2nd Floor
   San Francisco, CA  94107
   US

   Phone: +1 415 946 3800
   Email: msk@cloudmark.com









































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