Internet Message Access Protocol (IMAP) - SAVEDATE Extension
draft-bosch-imap-savedate-00

Versions: 00                                                            
Network Working Group                                           S. Bosch
Internet-Draft                                                Dovecot Oy
Intended status: Standards Track                      September 15, 2017
Expires: March 19, 2018


      Internet Message Access Protocol (IMAP) - SAVEDATE Extension
                      draft-bosch-imap-savedate-00

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

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   This Internet-Draft will expire on March 19, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   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 [FIXME: reference to SPECIAL-USE RFC for
   discussion on semantics of 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



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   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 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 by the IMAP
   COPY command, the save date attribute is not copied from the source
   message.  Instead, the current date and time 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 mailbox.

   For some mailboxes the underlying storage may not support the save
   date message attribute.  In such situations, the behavior is
   implementation-defined.  Using the internal date attribute instead is
   RECOMMENDED.  [FIXME: This is what Dovecot currently does, but for a
   standard this is inappropriate.  It should probably indicate the lack
   of support with a particular NO response code, or it could just
   return NULL or some other special value].








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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.

   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 three 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.

   Example:









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         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

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

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>.

8.  Acknowledgements

   Thanks to Alexey Melnikov and Michael Slusarz for reviews and
   suggestions.

   More reviews are appreciated.

9.  Normative References

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






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   [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.

Author's Address

   Stephan Bosch
   Dovecot Oy
   Lars Sonckin Kaari 10
   Espoo  02600
   Finland

   Email: stephan.bosch@dovecot.fi


































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