



EXTRA                                                           S. Bosch
Internet-Draft                                                Dovecot Oy
Intended status: Standards Track                             May 4, 2018
Expires: November 5, 2018


      Internet Message Access Protocol (IMAP) - SAVEDATE Extension
                   draft-ietf-extra-imap-savedate-01

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
   it extends the SEARCH command to allow using that attribute in
   searching criteria.

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
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   This Internet-Draft will expire on November 5, 2018.

Copyright Notice

   Copyright (c) 2018 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
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   to this document.  Code Components extracted from this document must



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   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 . . . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document extends 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 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 it 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 message 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
   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



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   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
   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 it was 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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

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 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 source mailbox remains unaffected; only
   the new copy of the message gets a new save date.  Consequently, when
   the 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 message attribute.  The handling of this situation is
   described in detail in the next section for each involved IMAP
   command.




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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.

   SAVEDATESUPPORTED
      Matches all messages in the mailbox when the underlying storage of
      that mailbox supports the save date attribute.  Conversely, it




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      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].

7.  IANA Considerations

   The IANA is requested to add "SAVEDATE" to the "IMAP Capabilities"
   registry located at <http://www.iana.org/assignments/imap-
   capabilities>.




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8.  Acknowledgements

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

9.  Normative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [IMAP-MOVE]
              Gulbrandsen, A. and N. Freed, "Internet Message Access
              Protocol (IMAP) - MOVE Extension", RFC 6851, January 2013.

   [IMAP4rev1]
              Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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>.

Author's Address

   Stephan Bosch
   Dovecot Oy
   Lars Sonckin Kaari 10
   Espoo  02600
   Finland

   Email: stephan.bosch@dovecot.fi















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