Vouch By Reference
RFC 5518

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Network Working Group                                         P. Hoffman
Request for Comments: 5518                                     J. Levine
Category: Standards Track                       Domain Assurance Council
                                                             A. Hathcock
                                                      Alt-N Technologies
                                                              April 2009

                           Vouch By Reference

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.

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   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Abstract

   This document describes the Vouch By Reference (VBR) protocol.  VBR
   is a protocol for adding third-party certification to email.  It
   permits independent third parties to certify the owner of a domain
   name that is associated with received mail.

Hoffman, et al.             Standards Track                     [Page 1]
RFC 5518                          VBR                         April 2009

Table of Contents

   1. Introduction ....................................................3
      1.1. Definitions ................................................4
   2. Use of the VBR-Info Header Field ................................4
   3. Validation Process ..............................................4
   4. The VBR-Info Header Field .......................................5
      4.1. Syntax of VBR-Info Header Fields ...........................5
   5. DNS Query .......................................................6
   6. Types of Message Content ........................................7
      6.1. All ........................................................8
      6.2. List .......................................................8
      6.3. Transaction ................................................8
   7. Obtaining a Useful Domain Name ..................................8
      7.1. DKIM .......................................................8
      7.2. DomainKeys .................................................9
      7.3. SPF ........................................................9
      7.4. Sender ID .................................................10
   8. Security Considerations ........................................10
   9. IANA Considerations ............................................10
   10. References ....................................................11
      10.1. Normative References .....................................11
      10.2. Informative References ...................................11
   Appendix A.  Acknowledgements .....................................12

Hoffman, et al.             Standards Track                     [Page 2]
RFC 5518                          VBR                         April 2009

1.  Introduction

   Vouch By Reference, or VBR, is a protocol for adding third-party
   certification to email.  Specifically, VBR permits independent third
   parties to certify the owner of a domain name that is associated with
   received mail.  VBR may be performed anywhere along the email transit
   path, by any capable receiving module, either within the handling
   service or by end-user software.

   VBR accomplishes this with a two-part protocol:

   o  In the first part, a sender affixes VBR information to email
      messages.  The VBR information says which domain certification
      services the sender believes will vouch for email traffic
      associated with that sender.

   o  In the second part, the receiver queries one or more certification