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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference 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 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Billon & Levine Expires 17 June 2022 [Page 1] Internet-Draft expires December 2021 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 Billon & Levine Expires 17 June 2022 [Page 2] Internet-Draft expires December 2021 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. Billon & Levine Expires 17 June 2022 [Page 3] Internet-Draft expires December 2021 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, . [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, . 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, . [RFC4021] Klyne, G. and J. Palme, "Registration of Mail and MIME Header Fields", RFC 4021, DOI 10.17487/RFC4021, March 2005, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Authors' Addresses Benjamin Billon Splio Email: bbillon@splio.com Billon & Levine Expires 17 June 2022 [Page 4] Internet-Draft expires December 2021 John Levine Standcore LLC Email: standards@standcore.com Billon & Levine Expires 17 June 2022 [Page 5]