The Require-Recipient-Valid-Since Header Field and SMTP Service Extension
RFC 7293

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Internet Engineering Task Force (IETF)                          W. Mills
Request for Comments: 7293                                   Yahoo! Inc.
Category: Standards Track                                   M. Kucherawy
ISSN: 2070-1721                                           Facebook, Inc.
                                                               July 2014

             The Require-Recipient-Valid-Since Header Field
                       and SMTP Service Extension

Abstract

   This document defines an extension for the Simple Mail Transfer
   Protocol (SMTP) called "RRVS" to provide a method for senders to
   indicate to receivers a point in time when the ownership of the
   target mailbox was known to the sender.  This can be used to detect
   changes of mailbox ownership and thus prevent mail from being
   delivered to the wrong party.  This document also defines a header
   field called "Require-Recipient-Valid-Since" that can be used to
   tunnel the request through servers that do not support the extension.

   The intended use of these facilities is on automatically generated
   messages, such as account statements or password change instructions,
   that might contain sensitive information, though it may also be
   useful in other applications.

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/rfc7293.

Mills & Kucherawy            Standards Track                    [Page 1]
RFC 7293              Require-Recipient-Valid-Since            July 2014

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
   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  The "RRVS" SMTP Extension . . . . . . . . . . . . . . . .   5
     3.2.  The "Require-Recipient-Valid-Since" Header Field  . . . .   5
     3.3.  Timestamps  . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Use By Generators . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Handling By Receivers . . . . . . . . . . . . . . . . . . . .   7
     5.1.  SMTP Extension Used . . . . . . . . . . . . . . . . . . .   7
       5.1.1.  Relays  . . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Header Field Used . . . . . . . . . . . . . . . . . . . .   9
       5.2.1.  Design Choices  . . . . . . . . . . . . . . . . . . .  10
     5.3.  Clock Synchronization . . . . . . . . . . . . . . . . . .  11
   6.  Relaying without RRVS Support . . . . . . . . . . . . . . . .  11
     6.1.  Header Field Conversion . . . . . . . . . . . . . . . . .  11
   7.  Header Field with Multiple Recipients . . . . . . . . . . . .  12
   8.  Special Use Addresses . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Mailing Lists . . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  Single-Recipient Aliases  . . . . . . . . . . . . . . . .  13
     8.3.  Multiple-Recipient Aliases  . . . . . . . . . . . . . . .  14
     8.4.  Confidential Forwarding Addresses . . . . . . . . . . . .  14
     8.5.  Suggested Mailing List Enhancements . . . . . . . . . . .  14
   9.  Continuous Ownership  . . . . . . . . . . . . . . . . . . . .  15
   10. Digital Signatures  . . . . . . . . . . . . . . . . . . . . .  15
   11. Authentication-Results Definitions  . . . . . . . . . . . . .  16
   12. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  SMTP Extension Example . . . . . . . . . . . . . . . . .  17
     12.2.  Header Field Example . . . . . . . . . . . . . . . . . .  17
     12.3.  Authentication-Results Example . . . . . . . . . . . . .  17

Mills & Kucherawy            Standards Track                    [Page 2]
RFC 7293              Require-Recipient-Valid-Since            July 2014