Internet DRAFT - draft-ietf-extra-imap-savedate
draft-ietf-extra-imap-savedate
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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 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
Provisions Relating to IETF Documents
(http://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
Bosch Expires November 5, 2018 [Page 1]
Internet-Draft IMAP - SAVEDATE Extension May 2018
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
Bosch Expires November 5, 2018 [Page 2]
Internet-Draft IMAP - SAVEDATE Extension May 2018
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.
Bosch Expires November 5, 2018 [Page 3]
Internet-Draft IMAP - SAVEDATE Extension May 2018
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
Bosch Expires November 5, 2018 [Page 4]
Internet-Draft IMAP - SAVEDATE Extension May 2018
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>.
Bosch Expires November 5, 2018 [Page 5]
Internet-Draft IMAP - SAVEDATE Extension May 2018
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
Bosch Expires November 5, 2018 [Page 6]
