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Updated Use of the Expires Message Header Field
draft-billon-expires-00

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Benjamin BILLON , John R. Levine
Last updated 2021-12-14
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draft-billon-expires-00
Network Working Group                                          B. Billon
Internet-Draft                                                     Splio
Intended status: Standards Track                               J. Levine
Expires: 17 June 2022                                      Standcore LLC
                                                        14 December 2021

            Updated Use of the Expires Message Header Field
                        draft-billon-expires-00

Abstract

   This document allows broader use of the Expires message header field.
   Senders can then indicate when a message sent becomes valueless and
   can safely be deleted.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 17 June 2022.

Copyright Notice

   Copyright (c) 2021 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 (https://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
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   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Header Field example  . . . . . . . . . . . . . . . . . . . .   2
   3.  Security considerations . . . . . . . . . . . . . . . . . . .   3
     3.1.  DKIM  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Implementation and Usage Consideration  . . . . . . . . . . .   3
     4.1.  Advice to senders . . . . . . . . . . . . . . . . . . . .   3
   5.  Advice to Receivers (Mailbox providers, Webmails and MUAs)  .   3
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [RFC4021] defines a number of header fields that can be added to
   Internet messages such as those used for mapping between X.400 and
   RFC822/MIME [RFC2156].  One of them is the Expires header field that
   provides the date and time at which a message is considered to lose
   its validity.

   The same principle can be applied to the Expires header field in a
   SMTP context, whether the message comes from a X.400 gateway as
   initially intended in [RFC2156], or from a RFC821/SMTP MTA.

   The date and time of expiration can be used by the mailbox provider
   or the MUA to indicate to the user that certain messages could be
   deleted, in an attempt to unclutter the user's mailbox and spare
   storage resources.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Header Field example

   The field definition and syntax remain the same.

   expires = "Expires" ":" date-time

   Example:

   Expires: Wed, 1 Dec 2021 17:22:57 +0000

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   There should be only one occurrence of the header field in a single
   message.  The presence of more than one Expires header would make
   them void.

3.  Security considerations

   The expiration of a message's validity should lead to the deletion of
   the message.  In certain cases, such as emails being used as proof or
   element of investigation, an early deletion may compromise the
   intended investigation.  For this reason, we want to avoid the header
   field to be tempered with.

3.1.  DKIM

   Senders including the Expires header field MUST sign the message with
   DKIM [RFC6376] and include the field in the h= tag.

   Receivers MUST NOT consider the value provided in the Expires header
   field if the DKIM check fails.

4.  Implementation and Usage Consideration

4.1.  Advice to senders

   Senders SHOULD add the header field along with a relevant date and
   time whenever applicable.

   Commercial newsletters are good candidates, especially when including
   time-limited offers.

   Social notification and one-time-password emails SHOULD include the
   Expires header field, with an expiration set within a few days at
   most.

   Payment receipts, bank statements, contracts and other emails that
   should be kept or archived by the recipient SHOULD NOT include the
   Expires header field.

5.  Advice to Receivers (Mailbox providers, Webmails and MUAs)

   Generally, no email should be automatically deleted solely based on
   the value of the Expires header field.

   The information provided in the header should be used as a signal
   that could be used to provide a feature or improved experience to the
   end-user.  Automation of email deletion based on the value of the
   Expires header may be set by the end-user.

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   Receivers can prevent deletion from happening if necessary.

   Presence of the Expires header field MUST NOT be interpreted as a
   sign of legitimacy.

6.  Acknowledgements

   This document was informed by discussions with and/or contributions
   from Jonathan Loriaux, Charles Sauthier and Simon Bressier.

7.  IANA Considerations

   This document has no IANA actions.

8.  Normative References

   [RFC2156]  Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay):
              Mapping between X.400 and RFC 822/MIME", RFC 2156,
              DOI 10.17487/RFC2156, January 1998,
              <https://www.rfc-editor.org/info/rfc2156>.

   [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
              "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
              RFC 6376, DOI 10.17487/RFC6376, September 2011,
              <https://www.rfc-editor.org/info/rfc6376>.

9.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4021]  Klyne, G. and J. Palme, "Registration of Mail and MIME
              Header Fields", RFC 4021, DOI 10.17487/RFC4021, March
              2005, <https://www.rfc-editor.org/info/rfc4021>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

   Benjamin Billon
   Splio

   Email: bbillon@splio.com

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   John Levine
   Standcore LLC

   Email: standards@standcore.com

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