DomainKeys Identified Mail (DKIM) Author Domain Signing Practices (ADSP)
RFC 5617

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Network Working Group                                          E. Allman
Request for Comments: 5617                                Sendmail, Inc.
Category: Standards Track                                      J. Fenton
                                                     Cisco Systems, Inc.
                                                               M. Delany
                                                             Yahoo! Inc.
                                                               J. Levine
                                                    Taughannock Networks
                                                             August 2009

DomainKeys Identified Mail (DKIM) Author Domain Signing Practices (ADSP)

Abstract

   DomainKeys Identified Mail (DKIM) defines a domain-level
   authentication framework for email to permit verification of the
   source and contents of messages.  This document specifies an adjunct
   mechanism to aid in assessing messages that do not contain a DKIM
   signature for the domain used in the author's address.  It defines a
   record that can advertise whether a domain signs its outgoing mail as
   well as how other hosts can access that record.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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 (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Allman, et al.              Standards Track                     [Page 1]
RFC 5617                          ADSP                       August 2009

Table of Contents

   1. Introduction ....................................................3
   2. Language and Terminology ........................................3
      2.1. Terms Imported from the DKIM Signatures Specification ......3
      2.2. Valid Signature ............................................4
      2.3. Author Address .............................................4
      2.4. Author Domain ..............................................4
      2.5. Alleged Author .............................................4
      2.6. Author Domain Signing Practices ............................4
      2.7. Author Domain Signature ....................................4
   3. Operation Overview ..............................................5
      3.1. ADSP Applicability .........................................5
      3.2. ADSP Usage .................................................6
      3.3. ADSP Results ...............................................6
   4. Detailed Description ............................................7
      4.1. DNS Representation .........................................7
      4.2. Publication of ADSP Records ................................7
           4.2.1. Record Syntax .......................................7
      4.3. ADSP Lookup Procedure ......................................9
   5. IANA Considerations ............................................10
      5.1. ADSP Specification Tag Registry ...........................10
      5.2. ADSP Outbound Signing Practices Registry ..................11
      5.3. Authentication-Results Method Registry Update .............11
      5.4. Authentication-Results Result Registry Update .............11
   6. Security Considerations ........................................13
      6.1. ADSP Threat Model .........................................14
      6.2. DNS Considerations ........................................14
      6.3. DNS Wildcards .............................................15
      6.4. Inappropriate Application of Author Domain Signatures .....15
   7. References .....................................................16
      7.1. Normative References ......................................16
      7.2. Informative References ....................................16
   Appendix A.  Lookup Examples ......................................17
     A.1.  Domain and ADSP Exist .....................................17
     A.2.  Domain Exists, ADSP Does Not Exist ........................17
     A.3.  Domain Does Not Exist .....................................17
   Appendix B.  Usage Examples .......................................18
     B.1.  Single Location Domains ...................................18
     B.2.  Bulk Mailing Domains ......................................18
     B.3.  Bulk Mailing Domains with Discardable Mail ................19