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Network Working Group                                           B. LeibaRequest for Comments: 2177               IBM T.J. Watson Research CenterCategory: Standards Track                                      June 1997IMAP4 IDLE commandStatus 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.1.   Abstract   The Internet Message Access Protocol [IMAP4] requires a client to   poll the server for changes to the selected mailbox (new mail,   deletions).  It's often more desirable to have the server transmit   updates to the client in real time.  This allows a user to see new   mail immediately.  It also helps some real-time applications based on   IMAP, which might otherwise need to poll extremely often (such as   every few seconds).  (While the spec actually does allow a server to   push EXISTS responses aysynchronously, a client can't expect this   behaviour and must poll.)   This document specifies the syntax of an IDLE command, which will   allow a client to tell the server that it's ready to accept such   real-time updates.2.   Conventions Used in this Document   In examples, "C:" and "S:" indicate lines sent by the client and   server respectively.   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"   in this document are to be interpreted as described inRFC 2060   [IMAP4].3.   Specification   IDLE Command   Arguments:  none   Responses:  continuation data will be requested; the client sends               the continuation data "DONE" to end the commandLeiba                       Standards Track                     [Page 1]

RFC 2177                   IMAP4 IDLE command                  June 1997   Result:     OK - IDLE completed after client sent "DONE"               NO - failure: the server will not allow the IDLE                    command at this time              BAD - command unknown or arguments invalid   The IDLE command may be used with any IMAP4 server implementation   that returns "IDLE" as one of the supported capabilities to the   CAPABILITY command.  If the server does not advertise the IDLE   capability, the client MUST NOT use the IDLE command and must poll   for mailbox updates.  In particular, the client MUST continue to be   able to accept unsolicited untagged responses to ANY command, as   specified in the base IMAP specification.   The IDLE command is sent from the client to the server when the   client is ready to accept unsolicited mailbox update messages.  The   server requests a response to the IDLE command using the continuation   ("+") response.  The IDLE command remains active until the client   responds to the continuation, and as long as an IDLE command is   active, the server is now free to send untagged EXISTS, EXPUNGE, and   other messages at any time.   The IDLE command is terminated by the receipt of a "DONE"   continuation from the client; such response satisfies the server's   continuation request.  At that point, the server MAY send any   remaining queued untagged responses and then MUST immediately send   the tagged response to the IDLE command and prepare to process other   commands. As in the base specification, the processing of any new   command may cause the sending of unsolicited untagged responses,   subject to the ambiguity limitations.  The client MUST NOT send a   command while the server is waiting for the DONE, since the server   will not be able to distinguish a command from a continuation.   The server MAY consider a client inactive if it has an IDLE command   running, and if such a server has an inactivity timeout it MAY log   the client off implicitly at the end of its timeout period.  Because   of that, clients using IDLE are advised to terminate the IDLE and   re-issue it at least every 29 minutes to avoid being logged off.   This still allows a client to receive immediate mailbox updates even   though it need only "poll" at half hour intervals.Leiba                       Standards Track                     [Page 2]

RFC 2177                   IMAP4 IDLE command                  June 1997   Example:    C: A001 SELECT INBOX               S: * FLAGS (Deleted Seen)               S: * 3 EXISTS               S: * 0 RECENT               S: * OK [UIDVALIDITY 1]               S: A001 OK SELECT completed               C: A002 IDLE               S: + idling               ...time passes; new mail arrives...               S: * 4 EXISTS               C: DONE               S: A002 OK IDLE terminated               ...another client expunges message 2 now...               C: A003 FETCH 4 ALL               S: * 4 FETCH (...)               S: A003 OK FETCH completed               C: A004 IDLE               S: * 2 EXPUNGE               S: * 3 EXISTS               S: + idling               ...time passes; another client expunges message 3...               S: * 3 EXPUNGE               S: * 2 EXISTS               ...time passes; new mail arrives...               S: * 3 EXISTS               C: DONE               S: A004 OK IDLE terminated               C: A005 FETCH 3 ALL               S: * 3 FETCH (...)               S: A005 OK FETCH completed               C: A006 IDLE4.   Formal Syntax   The following syntax specification uses the augmented Backus-Naur   Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4].   Non-terminals referenced but not defined below are as defined by   [IMAP4].   command_auth    ::= append / create / delete / examine / list / lsub /                       rename / select / status / subscribe / unsubscribe                       / idle                       ;; Valid only in Authenticated or Selected state   idle            ::= "IDLE" CRLF "DONE"Leiba                       Standards Track                     [Page 3]

RFC 2177                   IMAP4 IDLE command                  June 19975.   References   [IMAP4] Crispin, M., "Internet Message Access Protocol - Version   4rev1",RFC 2060, December 1996.6.   Security Considerations   There are no known security issues with this extension.7.   Author's Address   Barry Leiba   IBM T.J. Watson Research Center   30 Saw Mill River Road   Hawthorne, NY  10532   Email: leiba@watson.ibm.comLeiba                       Standards Track                     [Page 4]