Message Header Field for Indicating Message Authentication Status
RFC 7001

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Internet Engineering Task Force (IETF)                      M. Kucherawy
Request for Comments: 7001                                September 2013
Obsoletes: 5451, 6577
Category: Standards Track
ISSN: 2070-1721

   Message Header Field for Indicating Message Authentication Status

Abstract

   This document specifies a message header field called Authentication-
   Results for use with electronic mail messages to indicate the results
   of message authentication efforts.  Any receiver-side software, such
   as mail filters or Mail User Agents (MUAs), can use this header field
   to relay that information in a convenient and meaningful way to users
   or to make sorting and filtering decisions.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7001.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Kucherawy                    Standards Track                    [Page 1]
RFC 7001           Authentication-Results Header Field    September 2013

Table of Contents

   1. Introduction ....................................................3
      1.1. Purpose ....................................................4
      1.2. Trust Boundary .............................................5
      1.3. Processing Scope ...........................................6
      1.4. Requirements ...............................................6
      1.5. Definitions ................................................6
           1.5.1. Key Words ...........................................6
           1.5.2. Security ............................................6
           1.5.3. Email Architecture ..................................7
           1.5.4. Other Terms .........................................8
      1.6. Trust Environment ..........................................8
   2. Definition and Format of the Header Field .......................9
      2.1. General Description ........................................9
      2.2. Formal Definition ..........................................9
      2.3. The "policy" ptype ........................................12
      2.4. Authentication Identifier Field ...........................13
      2.5. Version Tokens ............................................14
      2.6. Defined Methods and Result Values .........................14
           2.6.1. DKIM and DomainKeys ................................14
           2.6.2. SPF and Sender ID ..................................15
           2.6.3. "iprev" ............................................17
           2.6.4. SMTP AUTH ..........................................17
           2.6.5. Other Registered Codes .............................18
           2.6.6. Extension Methods ..................................18
           2.6.7. Extension Result Codes .............................19
   3. The "iprev" Authentication Method ..............................19
   4. Adding the Header Field to a Message ...........................20
      4.1. Header Field Position and Interpretation ..................22
      4.2. Local Policy Enforcement ..................................23
   5. Removing Existing Header Fields ................................23
   6. IANA Considerations ............................................24
      6.1. The Authentication-Results Header Field ...................25
      6.2. "Email Authentication Methods" Registry ...................25
      6.3. "Email Authentication Result Names" Registry ..............26
   7. Security Considerations ........................................26
      7.1. Forged Header Fields ......................................26
      7.2. Misleading Results ........................................28
      7.3. Header Field Position .....................................28
      7.4. Reverse IP Query Denial-of-Service Attacks ................28