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A Property Types Registry for the Authentication-Results Header Field

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7410.
Author Murray Kucherawy
Last updated 2014-09-30 (Latest revision 2014-09-16)
Replaces draft-kucherawy-authres-ptypes-registry
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Scott Kitterman
Shepherd write-up Show Last changed 2014-09-15
IESG IESG state Waiting for AD Go-Ahead
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Barry Leiba
Send notices to,,
IANA IANA review state IANA - Not OK
Individual submission                                       M. Kucherawy
Internet-Draft                                        September 16, 2014
Updates: 7001 (if approved)
Intended status: Standards Track
Expires: March 20, 2015

 A Property Types Registry for the Authentication-Results Header Field


   This document updates RFC7001 by creating a registry for property
   types in the Authentication-Results header field, used in email
   authentication work, rather than limiting participants to using the
   original, small set of fixed values.

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

   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 March 20, 2015.

Copyright Notice

   Copyright (c) 2014 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
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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.  Updated 'ptype' Definition  . . . . . . . . . . . . . . . . . . 3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 5

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1.  Introduction

   [RFC7001] defines the email Authentication-Results header field that
   presents the results of an authentication effort in a machine-
   readable format.  The header field creates a place to collect the
   output from authentication processes that are disjoint from later
   processes that might use the output, such as analysis, filtering or
   sorting mechanisms.

   The specification in that document enumerated a small set of types of
   properties that can be reported using this mechanism.  There has
   emerged a desire to report types of properties about a message
   through this mechanism.  Accordingly, this document updates the
   specification to allow for additional property types ("ptypes")
   beyond the original set, and creates a registry where new ones can be
   listed and their defining documents referenced.

2.  Updated 'ptype' Definition

   Advanced Backus Naur Form (ABNF) is defined in [RFC5234].

   The ABNF in Section 2.2 of [RFC7001] is updated as follows:

       ptype = Keyword
             ; indicates whether the property being evaluated was
             ; a parameter to an [SMTP] command, was a value taken
             ; from a message header field, was some property of
             ; the message body, or was some other property evaluated by
             ; the receiving Message Transfer Agent (MTA)

   The ABNF token "Keyword" is defined in Section 4.1.2 of [RFC5321].

   Legal values of "ptype" are as defined in the IANA "Email
   Authentication Property Types" registry (see Section 3).  The initial
   values are as follows, matching those defined in [RFC7001]:

   body:  Indicates information that was extracted from the body of the
      message.  This might be an arbitrary string of bytes, a hash of a
      string of bytes, a Uniform Resource Identifier, or some other
      content of interest.

   header:  Indicates information that was extracted from the header of
      the message.  This might be the value of a header field or some
      portion of a header field.

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   policy:  A local policy mechanism was applied that augments or
      overrides the result returned by the authentication mechanism.
      See Section 2.3 of [RFC7001].

   smtp:  Indicates information that was extracted from an SMTP command
      that was used to relay the message.

   When a consumer of this header field encounters a ptype that it does
   not understand, it ignores the result reported with that ptype.

3.  IANA Considerations

   IANA is requested to create the Email Authentication Property Types
   registry.  Entries in this registry are subject to the Expert Review
   rules as described in [RFC5226].  Each entry in the registry requires
   the following values:

   o  The "ptype" token to be registered, which must fit within the ABNF
      described in Section 2.

   o  A brief description of what sort of information this "ptype" is
      meant to cover.

   o  An optional reference to the defining document.  This is
      recomended, but not required.

   The initial entries in this table are enumerated in Section 2.
   [RFC7001] should be listed as their defining document values.

   For new entries, the Designated Expert needs to assure that the
   description provided for the new entry adequately describes the
   intended use.  An example would be helpful to include in the entry's
   defining document, if any, although entries in the Email
   Authentication Methods registry or the Email Authentication Result
   Names registry might also serve as examples of intended use.

4.  Security Considerations

   It is unknown how legacy code, which expects one of a fixed set of
   "ptype" tokens, will handle new tokens as they begin to appear.
   There are typically two options: prevent delivery of the message, or
   ignore those portions of the field that use unknown "ptype" tokens
   and allow processing of the message to continue.

   The choice comes down to whether the consumer considers it a threat
   when there are unknown "ptypes" present.  The semantics of the report
   are unknown; the report might be indicating the message is authentic,
   fraudulent, or that a test failed to complete.  The report itself is

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   not actionable because it cannot be understood, and only its presence
   is certain.

   Generally, the advice in this situation is to ignore unknown
   "ptypes".  It is anticipated that a new property type evaluated by
   earlier handling agents would also result in the filtering of
   messages by those agents until consumers can be updated to interpret

5.  Normative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC7001]  Kucherawy, M., "Message Header Field for Indicating
              Message Authentication Status", RFC 7001, September 2013.

Appendix A.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this update: Dave Crocker, Tim Draegen,
   Scott Kitterman, Franck Martin.

Author's Address

   Murray S. Kucherawy
   270 Upland Drive
   San Francisco, CA  94127


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