Network Working Group M. Crispin
Request for Comments: 4315 December 2005
Category: Standards Track
Internet Message Access Protocol (IMAP) - UIDPLUS extension
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2005).
The UIDPLUS extension of the Internet Message Access Protocol (IMAP)
provides a set of features intended to reduce the amount of time and
resources used by some client operations. The features in UIDPLUS
are primarily intended for disconnected-use clients.
1. Introduction and Overview
The UIDPLUS extension is present in any IMAP server implementation
that returns "UIDPLUS" as one of the supported capabilities to the
The UIDPLUS extension defines an additional command. In addition,
this document recommends new status response codes in IMAP that
SHOULD be returned by all server implementations, regardless of
whether or not the UIDPLUS extension is implemented.
The added facilities of the features in UIDPLUS are optimizations;
clients can provide equivalent functionality, albeit less
efficiently, by using facilities in the base protocol.
1.1. Conventions Used in This Document
In examples, "C:" and "S:" indicate lines sent by the client and
Crispin Standards Track [Page 1]RFC 4315 IMAP - UIDPLUS Extension December 2005
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
be interpreted as described in [KEYWORDS].
A "UID set" is similar to the [IMAP] sequence set; however, the "*"
value for a sequence number is not permitted.
2. Additional Commands
The following command definition is an extension to [IMAP] section
2.1. UID EXPUNGE Command
Arguments: sequence set
Data: untagged responses: EXPUNGE
Result: OK - expunge completed
NO - expunge failure (e.g., permission denied)
BAD - command unknown or arguments invalid
The UID EXPUNGE command permanently removes all messages that both
have the \Deleted flag set and have a UID that is included in the
specified sequence set from the currently selected mailbox. If a
message either does not have the \Deleted flag set or has a UID
that is not included in the specified sequence set, it is not
This command is particularly useful for disconnected use clients.
By using UID EXPUNGE instead of EXPUNGE when resynchronizing with
the server, the client can ensure that it does not inadvertantly
remove any messages that have been marked as \Deleted by other
clients between the time that the client was last connected and
the time the client resynchronizes.
If the server does not support the UIDPLUS capability, the client
should fall back to using the STORE command to temporarily remove
the \Deleted flag from messages it does not want to remove, then
issuing the EXPUNGE command. Finally, the client should use the
STORE command to restore the \Deleted flag on the messages in
which it was temporarily removed.
Alternatively, the client may fall back to using just the EXPUNGE
command, risking the unintended removal of some messages.
Crispin Standards Track [Page 2]RFC 4315 IMAP - UIDPLUS Extension December 2005
Example: C: A003 UID EXPUNGE 3000:3002
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: * 3 EXPUNGE
S: A003 OK UID EXPUNGE completed
3. Additional Response Codes
The following response codes are extensions to the response codes
defined in [IMAP] section 7.1. With limited exceptions, discussed
below, server implementations that advertise the UIDPLUS extension
SHOULD return these response codes.
In the case of a mailbox that has permissions set so that the client