    Internet Engineering Task Force (IETF)                          S. Bosch
    Request for Comments: 8514                               Open Xchange Oy
    Category: Standards Track                                   January 2019
    ISSN: 2070-1721

          Internet Message Access Protocol (IMAP) - SAVEDATE Extension

    Abstract

       This document adds a new capability called "SAVEDATE" to the Internet
       Message Access Protocol (IMAP).  It defines a new IMAP message
       attribute called "save date" that, unlike the existing "internal
       date" attribute, always indicates the moment at which the message was
       saved in its current mailbox.  The SAVEDATE capability extends the
       FETCH command with the means to retrieve the save date attribute and
       extends the SEARCH command to allow using the save date attribute in
       searching criteria.

    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 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8514.

    Copyright Notice

       Copyright (c) 2019 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 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.

    Bosch                        Standards Track                    [Page 1]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
       2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
       3.  Save Date Message Attribute . . . . . . . . . . . . . . . . .   3
       4.  IMAP Protocol Changes . . . . . . . . . . . . . . . . . . . .   4
         4.1.  CAPABILITY Identification . . . . . . . . . . . . . . . .   4
         4.2.  FETCH Command and Response Extensions . . . . . . . . . .   4
         4.3.  SEARCH Command Extension  . . . . . . . . . . . . . . . .   4
       5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
       6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
       7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
       8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
       Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
       Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

    1.  Introduction

       This document extends the Internet Message Access Protocol (IMAP)
       [IMAP4rev1] with a new capability called "SAVEDATE".  This capability
       adds a new IMAP message attribute called "save date".  The save date
       is the date and time at which a message was saved in the mailbox in
       which it currently resides.  The save date is similar to the existing
       "internal date" attribute in that it is set at the time of delivery.
       However, the internal date attribute can be set to an arbitrary value
       for messages delivered to the mailbox using the APPEND command and is
       usually copied from the source message for messages delivered using
       the COPY command.  In contrast, the save date attribute is always set
       to the current date and time at the moment the message is saved in
       the mailbox, irrespective of how the message is delivered and from
       where it originates.

       The save date attribute is useful for implementing automated removal
       of messages from a mailbox after a configured amount of time.  For
       that application, it is necessary to know when the message was saved
       in the mailbox, which cannot be reliably determined using the
       internal date attribute.

       For example, a common client usage pattern is to move deleted
       messages to a Trash mailbox.  These messages are considered "deleted"
       at the time they are moved to the Trash mailbox.  In an effort to
       limit the size of the Trash mailbox, a client may subsequently desire
       to permanently remove (expunge) all messages in that Trash mailbox
       deleted before a certain time (e.g., a configurable expiration
       interval).  In that case, the internal date attribute cannot be used
       since it likely refers to the time at which the message was
       originally received.  The proper time comparison attribute should

    Bosch                        Standards Track                    [Page 2]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

       instead be the time at which the message was saved to the Trash
       mailbox.  Similar usage patterns can be observed for archiving
       solutions.

       The SAVEDATE capability extends the FETCH command and response to
       allow retrieving the date and time at which a message was saved.
       Also, the SAVEDATE capability extends the SEARCH command to allow
       searching messages with criteria based on when they were saved in the
       mailbox.

    2.  Conventions Used in This Document

       In examples, "C:" indicates lines sent by a client that is connected
       to a server.  "S:" indicates lines sent by the server to the client.

       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 [KEYWORDS] [KEYWORDS-UPD] when, and only when, they appear in
       all capitals, as shown here.

    3.  Save Date Message Attribute

       The save date message attribute is the date and time at which the
       message was saved in the mailbox it is now located in.  Unlike the
       internal date message attribute defined by [IMAP4rev1], this date and
       time value cannot be set arbitrarily when a message is delivered by
       the IMAP APPEND command.  Also, when a message is delivered to the
       mailbox by the IMAP COPY command [IMAP4rev1] or the IMAP MOVE command
       [IMAP-MOVE], the save date attribute is not copied from the source
       message.  Instead, the current date and time at which the message is
       delivered to a mailbox MUST be used to set the save date attribute.
       Once calculated, the save date attribute MUST NOT change as long as
       the message is contained within the same mailbox.

       This means that when the message is copied to another mailbox, the
       save date of the message in the source mailbox remains unaffected;
       only the new copy of the message gets a new save date.  Consequently,
       when the message is moved to another mailbox, either using the MOVE
       command or a command sequence involving the COPY command [IMAP-MOVE],
       the message always gets a new save date in the destination mailbox.

       For some specific mailboxes, the underlying storage may not support
       the save date attribute.  The handling of this situation is described
       in detail in the next section for each involved IMAP command.

    Bosch                        Standards Track                    [Page 3]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

    4.  IMAP Protocol Changes

    4.1.  CAPABILITY Identification

       IMAP servers that support this extension MUST include "SAVEDATE" in
       the response list to the CAPABILITY command.

    4.2.  FETCH Command and Response Extensions

       This extension defines one new data item for the FETCH command:

       SAVEDATE
          The save date of the message.

       This extension defines one new data item for the FETCH response:

       SAVEDATE
          A string representing the save date of the message.  However, if
          the underlying mailbox storage does not support the save date
          message attribute, the value returned for the SAVEDATE item is
          always NIL, rather than a string.

       Example:

             C: A101 FETCH 998 (SAVEDATE)
             S: * 998 FETCH (SAVEDATE "01-Jan-2015 18:50:53 +0100")
             S: A101 OK Fetch completed.

    4.3.  SEARCH Command Extension

       This extension defines four new search keys for the SEARCH command:

       SAVEDBEFORE <date>
          Messages whose save date (disregarding time and timezone) is
          earlier than the specified date.

       SAVEDON <date>
          Messages whose save date (disregarding time and timezone) is
          within the specified date.

       SAVEDSINCE <date>
          Messages whose save date (disregarding time and timezone) is
          within or later than the specified date.

    Bosch                        Standards Track                    [Page 4]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

       SAVEDATESUPPORTED
          Matches all messages in the mailbox when the underlying storage of
          that mailbox supports the save date attribute.  Conversely, it
          matches no messages in the mailbox when the save date attribute is
          not supported.

       When the underlying storage of a mailbox does not support the save
       date attribute, the SAVEDBEFORE, SAVEDON, and SAVEDSINCE search keys
       MUST use the internal date attribute instead.  In the context of the
       IMAP Multimailbox SEARCH Extension [MULTISEARCH], this fallback
       behavior MUST apply to each mailbox individually, meaning that only
       the mailboxes that lack support for the save date attribute use the
       internal date attribute instead.

       Example:

             C: A102 SEARCH SAVEDON 28-Dec-2014
             S: * SEARCH 993 994
             S: A102 OK Search completed.
             C: A103 SEARCH SAVEDSINCE 28-Dec-2014
             S: * SEARCH 993 994 995 996 997 998 999 1000 1001
             S: A103 OK Search completed.

    5.  Formal Syntax

       The following syntax specification augments the grammar specified in
       [IMAP4rev1].  It uses the Augmented Backus-Naur Form (ABNF) notation
       as specified in [ABNF].  Elements not defined here are taken from
       [IMAP4rev1].

       capability     =/ "SAVEDATE"

       fetch-att      =/ "SAVEDATE"

       msg-att-static =/ "SAVEDATE" SP (date-time / nil)

       search-key     =/ "SAVEDBEFORE" SP date /
                         "SAVEDON" SP date /
                         "SAVEDSINCE" SP date /
                         "SAVEDATESUPPORTED"

    6.  Security Considerations

       There are no known additional security issues with this extension
       beyond those described in the base protocol described in [IMAP4rev1].

    Bosch                        Standards Track                    [Page 5]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

    7.  IANA Considerations

       IANA has added "SAVEDATE" to the "IMAP Capabilities" registry located
       at <https://www.iana.org/assignments/imap-capabilities>.

    8.  Normative References

       [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
                  Specifications: ABNF", STD 68, RFC 5234,
                  DOI 10.17487/RFC5234, January 2008,
                  <https://www.rfc-editor.org/rfc/rfc5234>.

       [IMAP-MOVE]
                  Gulbrandsen, A. and N. Freed, "Internet Message Access
                  Protocol (IMAP) - MOVE Extension", RFC 6851,
                  DOI 10.17487/RFC6851, January 2013,
                  <https://www.rfc-editor.org/rfc/rfc6851>.

       [IMAP4rev1]
                  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
                  4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
                  <https://www.rfc-editor.org/rfc/rfc3501>.

       [KEYWORDS] 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/rfc/rfc2119>.

       [KEYWORDS-UPD]
                  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>.

       [MULTISEARCH]
                  Leiba, B. and A. Melnikov, "IMAP4 Multimailbox SEARCH
                  Extension", RFC 7377, DOI 10.17487/RFC7377, October 2014,
                  <https://www.rfc-editor.org/info/rfc7377>.

    Bosch                        Standards Track                    [Page 6]

    RFC 8514                IMAP - SAVEDATE Extension           January 2019

    Acknowledgements

       Thanks to Bron Gondwana, Alexey Melnikov, Timo Sirainen, and Michael
       Slusarz for reviews and suggestions.

    Author's Address

       Stephan Bosch
       Open Xchange Oy
       Lars Sonckin kaari 12
       Espoo  02600
       Finland

       Email: stephan.bosch@open-xchange.com

    Bosch                        Standards Track                    [Page 7]