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[mail-vet-discuss] Draft as of 5/31/2007

2007-05-31 18:16:57
...with most of the proposed changes to date, including Tony's (old) proposed re-vamp of the ABNF for the header itself and correspondingly adjusted examples.

Once we're approaching consensus, I'd like to submit this to the IETF to replace the one that's up there (although then I'll also have to post updates of all of our filters that use the header soon thereafter). I definitely want to do that sometime this month so that things are reasonably static by the time we head to Chicago.

Comments welcome.

-MSK



Individual submission                                       M. Kucherawy
Internet-Draft                                            Sendmail, Inc.
Intended status: Standards Track                            May 31, 2007
Expires: December 2, 2007


       Message Header for Indicating Sender Authentication Status
                 draft-kucherawy-sender-auth-header-05

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 2, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).












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Abstract

   This memo defines a new message header for use with electronic mail
   messages to indicate the results of sender authentication efforts.
   Mail user agents (MUAs) may use this message header to relay that
   information in a convenient way to users or to make sorting and
   filtering decisions.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Purpose  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Definition and Format of the Header  . . . . . . . . . . . . .  6
     2.1.  General Description  . . . . . . . . . . . . . . . . . . .  6
     2.2.  Formal Definition  . . . . . . . . . . . . . . . . . . . .  6
     2.3.  Authentication Identifier Fields . . . . . . . . . . . . .  8
     2.4.  Result Values  . . . . . . . . . . . . . . . . . . . . . .  9
     2.5.  Definition Of Initial Methods  . . . . . . . . . . . . . .  9
     2.6.  Extension Fields . . . . . . . . . . . . . . . . . . . . . 10
   3.  Adding The Header To A Message . . . . . . . . . . . . . . . . 11
     3.1.  Header Position and Interpretation . . . . . . . . . . . . 11
   4.  Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Removing The Header  . . . . . . . . . . . . . . . . . . . 13
   5.  Conformance and Usage Requirements . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
     6.1.  The Authentication-Results: header . . . . . . . . . . . . 15
     6.2.  Method Registry  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
     7.1.  Non-conformant MTAs  . . . . . . . . . . . . . . . . . . . 16
     7.2.  Header Position  . . . . . . . . . . . . . . . . . . . . . 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 18
   Appendix B.  Public Discussion . . . . . . . . . . . . . . . . . . 19
   Appendix C.  Legacy MUAs . . . . . . . . . . . . . . . . . . . . . 20
   Appendix D.  Authentication-Results Examples . . . . . . . . . . . 21
     D.1.  Trivial case; header not present . . . . . . . . . . . . . 21
     D.2.  Nearly-trivial case; service provided, but no
           authentication done  . . . . . . . . . . . . . . . . . . . 22
     D.3.  Service provided, authentication done  . . . . . . . . . . 22
     D.4.  Service provided, several authentications done, single
           MTA  . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     D.5.  Service provided, several authentications done,
           different MTAs . . . . . . . . . . . . . . . . . . . . . . 24



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   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26
   Intellectual Property and Copyright Statements . . . . . . . . . . 27

















































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1.  Introduction

   This memo defines a new message header for electronic mail messages
   which presents the results of a sender authentication effort in a
   machine-readable format.  The intent is to create a place to collect
   such data when sender authentication mechanisms are in use so that an
   MUA can provide a recommendation to the user as to the
   trustworthiness of the message's origin and content.

   This memo defines both the format of this new header, and discusses
   the implications of its presence or absence.

   [UPDATE PRIOR TO FINAL VERSION] At the time of publication of this
   draft, [AUTH], [DOMAINKEYS], [DKIM], [SENDERID] and [SPF] are the
   published e-mail authentication methods in common use.  As various
   methods emerge, it is necessary to prepare for their appearance and
   encourage convergence in the area of interfacing these filters to
   MUAs.

1.1.  Purpose

   The header defined in this memo is expected to serve several
   purposes:

   1.  Convey to MUAs from filters and MTAs the results of various
       sender authentication checks being applied;

   2.  Provide a common location for the presentation of this data;

   3.  Create an extensible framework for specifying new authentication
       methods as such emerge;

   4.  Convey the results of sender authentication tests to later
       filtering agents within the same "trust domain", as such agents
       might apply more or less stringent checks based on sender
       authentication results.

1.2.  Requirements

   This memo establishes no new requirements on existing protocols or
   servers, as there is currently no standard place for the described
   data to be collected or presented.

1.3.  Definitions

   This document occasionally uses terms that appear in capital letters.
   When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD
   NOT", and "MAY" appear capitalized, they are being used to indicate



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   particular requirements of this specification.  A discussion of the
   meanings of these terms appears in RFC2119.

   Generally it is assumed that the work of applying sender
   authentication schemes takes place at a border MTA, that is, an MTA
   which acts as a gateway between the general Internet and the users
   within an organizational boundary.  This specification is written
   with that assumption in mind.  However, there are some sites at which
   the entire mail infrastructure consists of a single host.  In such
   cases, such terms as "border MTA" and "delivery MTA" may well apply
   to the same machine or even the very same agent.








































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2.  Definition and Format of the Header

   This section gives a general overview of the format of the header
   being defined, and then provides more formal specification.

2.1.  General Description

   The new header being defined here is called "Authentication-Results".
   It is a Structured Header Field as defined in [MAIL] and thus all of
   the related definitions in that document apply.

   This new header MUST be added at the top of the message as it
   transits MTAs which do authentication checks so some idea of how far
   away the checks were done can be inferred.  It therefore should be
   treated as a Trace Header Field as defined in [MAIL] and thus all of
   the related definitions in that document apply.

   The decommented value of the header consists of an authentication
   identifier, some whitespace, a "property=value" statement indicating
   which property was selected to determine who sent the message and
   what value was extracted from that property, followed by zero or more
   authentication method names and a result associated with each,
   returned by the code that implements the method.

   As it is currently a matter of some debate, the header MAY appear
   more than once in a single message, or more than one result MAY be
   represented in a single header, or a combination of these MAY be
   applied.

2.2.  Formal Definition

   Formally, the header is specified as follows:

      header = "Authentication-Results:" [CFWS] authres-id CFWS
               *([CFWS] ";" methodspec propspec )


      authres-id = dot-atom-text
                 ; see below for a description of this element;
                 ; "dot-atom-text" is defined in section 3.2.4 of [MAIL]


      methodspec = [CFWS] method [CFWS] "=" [CFWS] result [CFWS]
                 ; indicates which authentication method was evaluated







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      propspec = ptype [CFWS] "." [CFWS] property [CFWS] "=" value
               ; an indication of which property of the message
               ; was evaluated by the authentication scheme being
               ; applied to yield the reported result


      method = token [ "/" version ]
             ; a method indicates which method's result is
             ; is represented by "value", and is one of the methods
             ; explicitly defined as valid in this document
             ; or is an extension method as defined below


      version = 1*( ALPHA / DIGIT ) 0*( "." 1*( ALPHA / DIGIT ) )
              ; indicates which version of the method was applied


      result = "pass" / "fail" / "softfail" / "neutral" /
                "temperror" / "permerror"
             ; an indication of the results of the attempt to
             ; authenticate the sender


      ptype = "smtp" / "header" / "body" / "policy"
            ; indicates whether the property being evaluated was
            ; a parameter to an [SMTP] command, or was a value taken
            ; from a message header, or was some property of the
            ; message body, or some other property evaluated by
            ; the receiving MTA


      property = token
              ; if "ptype" is "smtp", this indicates which [SMTP]
              ; command provided the value which was evaluated by the
              ; authentication scheme being applied; if "ptype" is
              ; "header", this indicates from which header the value
              ; being evaluated was extracted; if "ptype" is
              ; "body", this indicates the offset into the body at which
              ; content of interest was detected; if "ptype" is "policy"
              ; then this indicates the name of the policy which caused
              ; this header to be added (see below)


      value = [CFWS] token [CFWS] / mailbox
            ; the value extracted from the message property defined
            ; by the "ptype.property" construction; if the value
            ; identifies a mailbox, then it is a "mailbox"
            ; as defined in section 3.4 of [MAIL];



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            ; "mailbox" allows CFWS

   The "token" is as defined in Appendix A of [MIME].

   See Section 2.3 for a description of the "authres-id" element.

   The list of commands eligible for use with the "smtp" ptype can be
   found in [SMTP] and subsequent amendments.

   "CFWS" is as defined in section 3.2.3 of [MAIL].

   The "ptype" and "property" values used by each authentication method
   should be defined in the specification for that method (or its
   amendments).

   The "ptype" and "property" are case-insensitive.

   A "ptype" of "policy" indicates a policy decision about the message
   not specific to a property of the message that could be extracted.
   For example, if a method would normally report a "ptype.property" of
   "header.From" and no From: header was present, the method can use
   "policy" to indicate that no conclusion about the authenticity of the
   message could be reached.

   If the parsed "ptype.property" construction clearly identifies a
   mailbox (in particular, smtp.mail, smtp.rcpt, header.from,
   header.sender), then the "value" MUST be a "mailbox".  Other
   properties (e.g. smtp.helo) may be evaluated, but the property MUST
   still be expressed as a "token" for simplified parsing.

2.3.  Authentication Identifier Fields

   Every Authentication-Results header MUST have an authentication
   identifier field ("authres-id" above) which is a single result
   identifier.  This is similar in syntax to a fully-qualified domain
   name.

   The authentication identifier field provides a unique identifier that
   refers to the authenticating service within a given mail
   administrative domain.  The uniqueness of the identifier is
   guaranteed by the mail administrative domain that generates it and
   must pertain to exactly that one mail administrative domain.  This
   identifier is intended to be machine-readable and not necessarily
   meaningful to users.  MUAs may use this identifier to determine
   whether or not the data contained in an Authentication-Results header
   can be trusted.

   The mail administrative domain's unique domain name MUST be used as



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   the last portion of the identifier.

   Examples of valid authentication identifiers are mail.example.org,
   engineering.example.edu and ms1.newyork.example.com.

2.4.  Result Values

   The six possible values of the "result" are:

   pass:  The message passed the authentication tests.  (This may
      require accessing an authentication policy of some kind published
      by the sending domain.)

   hardfail:  The message failed the authentication tests.  (This may
      require accessing an authentication policy of some kind published
      by the sending domain.)

   softfail:  The authentication method has either an explicit
      (published by the sending domain) or implicit policy, but the
      policy being used doesn't require successful authentication of all
      messages from that domain, and the message failed the
      authentication tests.

   neutral:  The authentication method completed without errors, but was
      unable to reach either a positive or negative result about the
      message.

   temperror:  A temporary (recoverable) error occurred attempting to
      authenticate the sender; either the process couldn't be completed
      locally, or (for methods requiring a policy to be accessed) there
      was a temporary failure retrieving the sending domain's policy.  A
      later retry may produce a more final result.

   permerror:  A permanent (unrecoverable) error occurred attempting to
      authenticate the sender; either the process couldn't be completed
      locally, or (for methods requiring a policy to be accessed) there
      was a permanent failure retrieving the sending domain's policy.  A
      later retry is unlikely to yield a final result.

   New methods not specified in this document MUST indicate which of
   these should be returned when exceptions such as syntax errors are
   detected.

2.5.  Definition Of Initial Methods

   As they are currently existing specifications for sender
   authentication, it is appropriate to define an authentication method
   identifier for each of [AUTH], [DOMAINKEYS], [DKIM], [SENDERID] and



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   [SPF].  Therefore, the authentication method identifiers "auth",
   "domainkeys", "dkim", "senderid" and "spf" respectively are hereby
   defined for MTAs applying those specifications for e-mail sender
   authentication.  See Section 6 for details.

2.6.  Extension Fields

   Additional authentication method identifiers may be defined in the
   future by later revisions or extensions to this specification.
   Extension identifiers beginning with "x-" will never be defined as
   standard fields; such names are reserved for experimental use.
   Method identifiers NOT beginning with "x-" MUST be registered with
   the Internet Assigned Numbers Authority (IANA) and published in an
   RFC.

   Extension identifiers may be defined for the following reasons:

   1.  To allow additional information from emergent authentication
       systems to be communicated to MUAs.  The names of such
       identifiers should reflect the name of the method being defined,
       but should not be needlessly long.

   2.  To allow the creation of "sub-identifiers" which indicate
       different levels of authentication and differentiate between
       their relative strengths, e.g. "auth1-weak" and "auth1-strong".

   Authentication method implementors are encouraged to provide adequate
   information, via [MAIL] comments if necessary, to allow an MUA
   developer to understand or relay ancilliary details of authentication
   results.  For example, if it might be of interest to relay what data
   was used to perform an evaluation, such information could be relayed
   as a comment in the header, such as:

      Authentication-Results: mx.example.com; foo=pass (2 of 3 tests OK)

















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3.  Adding The Header To A Message

   This specification makes no attempt to evaluate the relative
   strengths of various sender authentication methods that may become
   available.  As such, the order of the presented authentication
   methods and results MUST NOT be used to determine the importance or
   strength of any given method over another.  Instead, the MUA must
   interpret the result of each method based on its knowledge of what
   that method evaluates.

   The "method" MUST refer to an authentication method declared in this
   memo, or in a subsequent one, or to an authentication method name
   assigned by IANA.

   An MTA compliant with this specification MUST add this header (after
   performing one or more sender authentication tests) to indicate at
   which host the test was done, which test got applied and what the
   result was.  If an MTA applies more than one such test, it MUST
   either add this header once per test, or one header indicating all of
   the results.  An MTA MUST NOT add a result to an existing header.

   For security reasons, a border MTA conforming to this specification
   MUST delete any discovered instance of this header which claims to
   have been added within its trust boundary.  For example, a border MTA
   for example.com receiving a message from outside of its mail domain
   MUST delete any instance of this header bearing an authentication
   identifier indicating the header was added within that domain prior
   to adding its own headers.  This applies in both directions so that
   hosts outside the domain cannot claim results MUAs inside the domain
   might trust.  However, care must be taken not to remove headers added
   on messages which remain entirely within the originator's trust
   boundary (i.e. local-to-local mail).

   An MTA MAY add this header containing only the authentication
   identifier portion to indicate explicitly that no sender
   authentication schemes were applied prior to delivery of this
   message.

3.1.  Header Position and Interpretation

   In order to ensure non-ambiguous results and avoid the impact of
   false headers, an MUA SHOULD NOT interpret this header unless
   specifically instructed to do so by the user.  That is, this should
   not be "on by default".  Naturally then, users would not activate
   such a feature unless they are certain the header will be added by
   the receiving MTA that accepts the mail which is ultimately read by
   the MUA, and instances of the header added by foreign MTAs will be
   removed before delivery.



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   Furthermore, an MUA SHOULD NOT interpret this header unless the
   hostname it bears appears to be one within its own trust domain as
   configured by the user.

   An MUA should not reveal these results to naive end users unless the
   results are accompanied by, at a minimum, some associated reputation
   data about the sender which was authenticated.

   As stated in Section 2.1, this header field SHOULD be treated as
   though it were a trace header field as defined in section 3.6 of
   [MAIL], and hence SHOULD not be reordered and SHOULD be prepended to
   the message, so that there is generally some indication upon delivery
   of where in the chain of handling MTAs the sender authentcation was
   done.

   Further discussion of this can be found in the Security
   Considerations section below.


































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4.  Discussion

   This section discusses various implementation issues not specifically
   related to security.  Security issues are discussed in a later
   section.

4.1.  Removing The Header

   As specified in Section 3, instances of this header added by outside
   MTAs which appear to come from inside an MTA's trust boundary must be
   removed.  In the case of messages signed using [DKIM] or other
   message signing methods which sign headers, this may invalidate one
   or more signature on the message if they included the header to be
   removed at the time of signing.  This behaviour is desirable since
   there's no value in validating the signature on a message with forged
   headers.  However, signing agents MAY elect to omit these headers
   from signing to avoid this situation.


































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5.  Conformance and Usage Requirements

   An MTA or gateway conforms to this specification if it applies one or
   more sender authentication mechanisms and inserts a header
   corresponding to this specification after doing so and prior to
   delivery.

   MTAs that are relaying mail rather than delivering it, i.e. are not
   part of an intended recipient's trust boundary, MAY perform sender
   authentication or even take actions based on the results found, but
   SHOULD NOT add an "Authentication-Results" header if relaying rather
   than rejecting or discarding at the gateway.  Conversely, an MTA
   doing local delivery and some form of sender authentication MUST add
   this header prior to delivery the message in order to be compliant.

   A minimal implementation which does at least one sender
   authentication check will add the header defined by this memo prior
   to invoking local delivery procedures.

   This specification places no restrictions on the processing of the
   header's contents by user agents or distribution lists.  It is
   presented to those packages solely for their own information.





























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6.  IANA Considerations

   This specification introduces some new namespaces that will be
   registered with IANA.  In all cases, new entries are assigned only
   for values that have been documented in a published RFC that has IETF
   Consensus, per [IANA-CONSIDERATIONS].

6.1.  The Authentication-Results: header

   Per [IANA-HEADERS], the "Authentication-Results:" header field is
   added to the IANA Permanent Message Header Field Registry.  The
   following is the registration template:

     Header field name: Authentication-Results
     Applicable protocol: mail ([RFC2822])
     Status: Standard
     Author/Change controller: IETF
     Specification document(s): [TBD]
     Related information:
       Requesting review of any proposed changes and additions to
       this field is recommended.

6.2.  Method Registry

   As stated above, names of sender authentication methods supported by
   this specification must be registered with IANA, with the exception
   of experimental names as described above.

   Each method must register a name, the specification which defines it,
   which "ptype" is appropriate for use with that method, and which
   "property" should be reported by that method.

   The initial set of entries in this registry is as follows:

   +------------+---------+--------+----------------------------+
   |   Method   | defined | ptype  | property                   |
   +------------+---------+--------+----------------------------+
   |    auth    | RFC2554 | smtp   | auth                       |
   +------------+---------+--------+----------------------------+
   | domainkeys | RFC4870 | header | From or Sender             |
   +------------+---------+--------+----------------------------+
   |    dkim    | RFC4871 | header | value of signature "i" tag |
   +------------+---------+--------+----------------------------+
   |  senderid  | RFC4406 | header | name of header used by PRA |
   +------------+---------+--------+----------------------------+
   |     spf    | RFC4408 | smtp   | from                       |
   +------------+---------+--------+----------------------------+




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7.  Security Considerations

   The following security considerations apply when applying or
   processing the "Authentication-Results" header:

7.1.  Non-conformant MTAs

   An MUA that is aware of this specification which accesses a mailbox
   whose mail is handled by a non-conformant MTA is in a position to
   make false conclusions based on forged headers.  A malicious user or
   agent could forge a header using the destination MX for a receiving
   domain as the hostname token in the value of the header, and with the
   rest of the value claim that the sender was properly authenticated.
   The non-conformant MTA would fail to strip the forged header, and the
   MUA could inappropriately trust it.

   It is for this reason an MUA SHOULD NOT have processing of the
   "Authentication-Results" header enabled by default; instead it must
   be ignored, at least for the purposes of enacting filtering
   decisions, unless specifically enabled by the user after verifying
   that the MTA is compliant.  It is acceptable to have an MUA aware of
   this standard, but have an explicit list of hostnames whose
   "Authentication-Results" headers are trustworthy, however this list
   SHOULD initially be empty.

   Proposed alternate solutions to this problem are nascent.  Possibly
   the simplest is a digital signature on the header which can be
   verified by a posted public key.  Another would be a means to
   interrogate the MTA that added the header to see if it is actually
   providing any sender authentication services and saw the message in
   question, but this isn't especially palatable.  In either case, a
   method needs to exist to verify that the host which appears to have
   added the header (a) actually did so, and (b) is legitimately adding
   that header for this delivery.

7.2.  Header Position

   Despite the requirements of [MAIL], headers can sometimes be
   reordered enroute by intermediate MTAs.  The goal of requiring header
   addition only at the top of a message is an acknowledgement that some
   MTAs do reorder headers, but most do not.  Thus, in the general case,
   there will be some indication of which MTAs (if any) handled the
   message after the addition of the header defined here.








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8.  References

8.1.  Normative References

   [MAIL]     Resnick, P., "Internet Message Format", RFC 2822,
              April 2001.

   [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

8.2.  Informative References

   [AUTH]     Myers, J., "SMTP Service Extension for Authentication",
              RFC 2554, March 1999.

   [DKIM]     Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
              J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
              Signatures", RFC 4817, May 2007.

   [DOMAINKEYS]
              Delany, M., "Domain-based Email Authentication Using
              Public Keys Advertised in the DNS (DomainKeys)", RFC 4870,
              May 2007.

   [IANA-CONSIDERATIONS]
              Alvestrand, H. and T. Narten, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 2434,
              October 1998.

   [IANA-HEADERS]
              Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", RFC 2434,
              September 2004.

   [SENDERID]
              Lyon, J. and M. Wong, "Sender ID: Authenticating E-Mail",
              RFC 4406, April 2006.

   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.

   [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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Appendix A.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this proposal: Tony Hansen of AT&T, Mark
   Delany and Miles Libbey of Yahoo!  Inc., Jim Fenton of Cisco, and
   Eric Allman of Sendmail, Inc.













































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Appendix B.  Public Discussion

   Public discussion of this proposed specification is handled via the
   mail-vet-discuss(_at_)mipassoc(_dot_)org mailing list.  The list is open.
   Access to subscription forms and to list archives can be found at
   http://mipassoc.org/mailman/listinfo/mail-vet-discuss.













































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Appendix C.  Legacy MUAs

   Implementors of this proposal should be aware that many MUAs are
   unlikely to be retrofit to support the new header and its semantics.
   In the interests of convenience and quicker adaptation, a delivery
   MTA might want to consider adding things that are processed by
   existing MUAs as well as the header defined by this specification.
   One suggestion is to include a Priority: header, on messages which
   don't already have such a header, containing a value that reflects
   the strength of the authentication that was accomplished, e.g. "low"
   for weak or no authentication, "normal" or "high" for good
   authentication.

   Certainly some modern MUAs can filter based on the content of this
   header, but as there is keen interest in having MUAs make some kind
   of graphical representation of this header's meaning, other interim
   means of doing so may be necessary while this proposal is adopted.


































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Appendix D.  Authentication-Results Examples

   This section presents some examples of the use of this header to
   indicate authentication results.

D.1.  Trivial case; header not present

   The trivial case:

        From: sender(_at_)example(_dot_)com
        Received: from mail-router.example.com
                      (mail-router.example.com [1.2.3.4])
                  by server.sendmail.com (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: receiver(_at_)sendmail(_dot_)com
        Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
        Subject: here's a sample

        Hello!  Goodbye!

   Example 1: Trivial case

   The "Authentication-Results" header is completely absent.  The MUA
   may make no conclusion about the validity of the message.  This could
   be the case because the sender authentication services were not
   available at the time of delivery, or no service is provided, or the
   MTA is not in compliance with this specification.






















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D.2.  Nearly-trivial case; service provided, but no authentication done

   A message that was delivered by an MTA which conforms to this
   standard but provides no actual sender authentication service:

        Authentication-Results: mail-router.example.com
        From: sender(_at_)example(_dot_)com
        Received: from mail-router.example.com
                      (mail-router.example.com [1.2.3.4])
                  by server.sendmail.com (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: receiver(_at_)sendmail(_dot_)com
        Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
        Subject: here's a sample

        Hello!  Goodbye!

   Example 2: Header present but no authentication done

   The "Authentication-Results" header is present, indicating that the
   delivering MTA (which is named in the value of the header) conforms
   to this specification.  The absence of any method and result tokens
   indicates that no sender authentication was done.

D.3.  Service provided, authentication done

   A message that was delivered by an MTA which conforms to this
   standard and applied some sender authentication:

        Authentication-Results: mail-router.example.com;
                  auth=pass (cram-md5) 
smtp(_dot_)auth=sender(_at_)example(_dot_)com
        From: sender(_at_)example(_dot_)com
        Received: from dialup-1-2-3-4.example-isp.com
                      (dialup-1-2-3-4.example-isp.com [1.2.3.4])
                  by mail-router.example.com (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: receiver(_at_)sendmail(_dot_)com
        Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
        Subject: here's a sample

        Hello!  Goodbye!

   Example 3: Header reporting results




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   The "Authentication-Results" header is present, indicating that the
   delivering MTA (which is identified in the value of the header)
   conforms to this specification.  Furthermore, the sender
   authenticated herself/himself to the MTA via a method specified in
   [AUTH].  The actual method is identified in a header comment after
   the method's result is indicated.  The MUA could extract and relay
   this extra information if desired.

D.4.  Service provided, several authentications done, single MTA

   A message that was relayed inbound via a single MTA which conforms to
   this standard and applied two different sender authentication checks:

        Authentication-Results: mail-router.example.com;
                  auth=pass (cram-md5) 
smtp(_dot_)mail=sender(_at_)example(_dot_)com;
                  spf=pass smtp(_dot_)mail=sender(_at_)example(_dot_)com
        Authentication-Results: mail-router.example.com;
                  sender-id=pass header(_dot_)from=sender(_at_)example(_dot_)com
        From: sender(_at_)example(_dot_)com
        Received: from mail-router.example.com
                      (mail-router.example.com [1.2.3.4])
                  by dialup-1-2-3-4.example-isp.com (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: receiver(_at_)sendmail(_dot_)com
        Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
        Subject: here's a sample

        Hello!  Goodbye!

   Example 4: Headers reporting results from one MTA

   The "Authentication-Results" header is present, indicating the
   delivering MTA (which is identified in the value of the header)
   conforms to this specification.  Furthermore, the sender
   authenticated herself/himself to the MTA via a method specified in
   [AUTH], and both [SPF] and [SENDERID] checks were done and passed.
   The MUA could extract and relay this extra information if desired.

   Two "Authentication-Results" headers are not required since the same
   host did all of the checking.  The authenticating agent could have
   consolidated all the results into one header.








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D.5.  Service provided, several authentications done, different MTAs

   A message that was relayed inbound by two different MTAs which
   conform to this standard and applied multiple sender authentication
   checks:

        Authentication-Results: auth-checker.example.com;
                  sender-id=pass 
header(_dot_)from=sender(_at_)example(_dot_)com;
                  dkim=pass (good signature) 
header(_dot_)i=sender(_at_)example(_dot_)com
        Received: from mail-router.example.com
                      (mail-router.example.com [10.11.12.13])
                  by auth-checker.example.com (8.11.6/8.11.6)
                      with ESMTP id i7PK0sH7021929;
                  Fri, Feb 15 2002 17:19:22 -0800
        Authentication-Results: mail-router.example.com;
                  auth=pass (cram-md5) 
smtp(_dot_)mail=sender(_at_)example(_dot_)com;
                  spf=fail smtp(_dot_)mail=sender(_at_)example(_dot_)com
        Received: from dialup-1-2-3-4.example-isp.com
                      (dialup-1-2-3-4.example-isp.com [1.2.3.4])
                  by mail-router.example.com (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        DKIM-Signature: a=rsa-sha1; s=gatsby; d=example.com;
                  c=simple; q=dns;
                  b=EToRSuvUfQVP3Bkz ... rTB0t0gYnBVCM=
        From: sender(_at_)example(_dot_)com
        Date: Fri, Feb 15 2002 16:54:30 -0800
        To: receiver(_at_)sendmail(_dot_)com
        Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
        Subject: here's a sample

        Hello!  Goodbye!

   Example 5: Headers reporting results from multiple MTAs

   The "Authentication-Results" header is present, indicating
   conformance to this specification.  It is present twice because two
   different MTAs in the chain of delivery did authentication tests.
   The first, "mail-router.example.com" reports that [AUTH] and [SPF]
   were both used, and [AUTH] passed but [SPF] failed.  In the [AUTH]
   case, additional data is provided in the comment field, which the MUA
   can choose to render if desired.

   The second MTA, identifying itself as "auth-checker.example.com",
   reports that it did a [SENDERID] test and a [DKIM] test, both of
   which passed.  Again, additional data about one of the tests is
   provided as a comment, which the MUA may choose to render.




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   Since different hosts did the two sets of authentication checks, the
   headers cannot be consolidated in this example.

















































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Author's Address

   Murray S. Kucherawy
   Sendmail, Inc.
   6425 Christie Ave., Suite 400
   Emeryville, CA  94608
   US

   Phone: +1 510 594 5400
   Email: msk+ietf(_at_)sendmail(_dot_)com









































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Full Copyright Statement

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