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+Network Working Group B. Leiba
+Request for Comments: 2177 IBM T.J. Watson Research Center
+Category: Standards Track June 1997
+
+
+ IMAP4 IDLE command
+
+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.
+
+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 in RFC 2060
+ [IMAP4].
+
+3. Specification
+
+ IDLE Command
+
+ Arguments: none
+
+ Responses: continuation data will be requested; the client sends
+ the continuation data "DONE" to end the command
+
+
+
+Leiba Standards Track [Page 1]
+
+RFC 2177 IMAP4 IDLE command June 1997
+
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+ 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.
+
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+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 IDLE
+
+4. 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"
+
+
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+Leiba Standards Track [Page 3]
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+RFC 2177 IMAP4 IDLE command June 1997
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+5. 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.com
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+Leiba Standards Track [Page 4]
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