Request for Comments: 8514
Category: Standards Track
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Internet Message Access Protocol (IMAP) - SAVEDATE Extension
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.
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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 . . . . . . . . . . . . . . . . . . . . . 6 8. Normative References . . . . . . . . . . . . . . . . . . . . 6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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 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.
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:
The save date of the message.
This extension defines one new data item for the FETCH response:
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.
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:
Messages whose save date (disregarding time and timezone) is earlier than the specified date.
Messages whose save date (disregarding time and timezone) is within the specified date.
Messages whose save date (disregarding time and timezone) is within or later than the specified date.
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.
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
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>.
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>.
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>.
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>.
Thanks to Bron Gondwana, Alexey Melnikov, Timo Sirainen, and Michael Slusarz for reviews and suggestions.
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