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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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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