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+Network Working Group M. Gahrns
+Request for Comments: 2342 Microsoft
+Category: Standards Track C. Newman
+ Innosoft
+ May 1998
+
+
+ IMAP4 Namespace
+
+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 Notice
+
+ Copyright (C) The Internet Society (1998). All Rights Reserved.
+
+1. Abstract
+
+ IMAP4 [RFC-2060] does not define a default server namespace. As a
+ result, two common namespace models have evolved:
+
+ The "Personal Mailbox" model, in which the default namespace that is
+ presented consists of only the user's personal mailboxes. To access
+ shared mailboxes, the user must use an escape mechanism to reach
+ another namespace.
+
+ The "Complete Hierarchy" model, in which the default namespace that
+ is presented includes the user's personal mailboxes along with any
+ other mailboxes they have access to.
+
+ These two models, create difficulties for certain client operations.
+ This document defines a NAMESPACE command that allows a client to
+ discover the prefixes of namespaces used by a server for personal
+ mailboxes, other users' mailboxes, and shared mailboxes. This allows
+ a client to avoid much of the manual user configuration that is now
+ necessary when mixing and matching IMAP4 clients and servers.
+
+2. Conventions used in this document
+
+ In examples, "C:" and "S:" indicate lines sent by the client and
+ server respectively. If such lines are wrapped without a new "C:" or
+ "S:" label, then the wrapping is for editorial clarity and is not
+ part of the command.
+
+
+
+Gahrns & Newman Standards Track [Page 1]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ Personal Namespace: A namespace that the server considers within the
+ personal scope of the authenticated user on a particular connection.
+ Typically, only the authenticated user has access to mailboxes in
+ their Personal Namespace. It is the part of the namespace that
+ belongs to the user that is allocated for mailboxes. If an INBOX
+ exists for a user, it MUST appear within the user's personal
+ namespace. In the typical case, there SHOULD be only one Personal
+ Namespace on a server.
+
+ Other Users' Namespace: A namespace that consists of mailboxes from
+ the Personal Namespaces of other users. To access mailboxes in the
+ Other Users' Namespace, the currently authenticated user MUST be
+ explicitly granted access rights. For example, it is common for a
+ manager to grant to their secretary access rights to their mailbox.
+ In the typical case, there SHOULD be only one Other Users' Namespace
+ on a server.
+
+ Shared Namespace: A namespace that consists of mailboxes that are
+ intended to be shared amongst users and do not exist within a user's
+ Personal Namespace.
+
+ The namespaces a server uses MAY differ on a per-user basis.
+
+ 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 [RFC-2119].
+
+3. Introduction and Overview
+
+ Clients often attempt to create mailboxes for such purposes as
+ maintaining a record of sent messages (e.g. "Sent Mail") or
+ temporarily saving messages being composed (e.g. "Drafts"). For
+ these clients to inter-operate correctly with the variety of IMAP4
+ servers available, the user must enter the prefix of the Personal
+ Namespace used by the server. Using the NAMESPACE command, a client
+ is able to automatically discover this prefix without manual user
+ configuration.
+
+ In addition, users are often required to manually enter the prefixes
+ of various namespaces in order to view the mailboxes located there.
+ For example, they might be required to enter the prefix of #shared to
+ view the shared mailboxes namespace. The NAMESPACE command allows a
+ client to automatically discover the namespaces that are available on
+ a server. This allows a client to present the available namespaces to
+ the user in what ever manner it deems appropriate. For example, a
+
+
+
+
+
+
+Gahrns & Newman Standards Track [Page 2]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ client could choose to initially display only personal mailboxes, or
+ it may choose to display the complete list of mailboxes available,
+ and initially position the user at the root of their Personal
+ Namespace.
+
+ A server MAY choose to make available to the NAMESPACE command only a
+ subset of the complete set of namespaces the server supports. To
+ provide the ability to access these namespaces, a client SHOULD allow
+ the user the ability to manually enter a namespace prefix.
+
+4. Requirements
+
+ IMAP4 servers that support this extension MUST list the keyword
+ NAMESPACE in their CAPABILITY response.
+
+ The NAMESPACE command is valid in the Authenticated and Selected
+ state.
+
+5. NAMESPACE Command
+
+ Arguments: none
+
+ Response: an untagged NAMESPACE response that contains the prefix
+ and hierarchy delimiter to the server's Personal
+ Namespace(s), Other Users' Namespace(s), and Shared
+ Namespace(s) that the server wishes to expose. The
+ response will contain a NIL for any namespace class
+ that is not available. Namespace_Response_Extensions
+ MAY be included in the response.
+ Namespace_Response_Extensions which are not on the IETF
+ standards track, MUST be prefixed with an "X-".
+
+ Result: OK - Command completed
+ NO - Error: Can't complete command
+ BAD - argument invalid
+
+ Example 5.1:
+ ===========
+
+ < A server that supports a single personal namespace. No leading
+ prefix is used on personal mailboxes and "/" is the hierarchy
+ delimiter.>
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) NIL NIL
+ S: A001 OK NAMESPACE command completed
+
+
+
+
+
+Gahrns & Newman Standards Track [Page 3]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ Example 5.2:
+ ===========
+
+ < A user logged on anonymously to a server. No personal mailboxes
+ are associated with the anonymous user and the user does not have
+ access to the Other Users' Namespace. No prefix is required to
+ access shared mailboxes and the hierarchy delimiter is "." >
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE NIL NIL (("" "."))
+ S: A001 OK NAMESPACE command completed
+
+ Example 5.3:
+ ===========
+
+ < A server that contains a Personal Namespace and a single Shared
+ Namespace. >
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) NIL (("Public Folders/" "/"))
+ S: A001 OK NAMESPACE command completed
+
+ Example 5.4:
+ ===========
+
+ < A server that contains a Personal Namespace, Other Users'
+ Namespace and multiple Shared Namespaces. Note that the hierarchy
+ delimiter used within each namespace can be different. >
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) (("~" "/")) (("#shared/" "/")
+ ("#public/" "/")("#ftp/" "/")("#news." "."))
+ S: A001 OK NAMESPACE command completed
+
+ The prefix string allows a client to do things such as automatically
+ creating personal mailboxes or LISTing all available mailboxes within
+ a namespace.
+
+ Example 5.5:
+ ===========
+
+ < A server that supports only the Personal Namespace, with a
+ leading prefix of INBOX to personal mailboxes and a hierarchy
+ delimiter of ".">
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("INBOX." ".")) NIL NIL
+ S: A001 OK NAMESPACE command completed
+
+
+
+Gahrns & Newman Standards Track [Page 4]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ < Automatically create a mailbox to store sent items.>
+
+ C: A002 CREATE "INBOX.Sent Mail"
+ S: A002 OK CREATE command completed
+
+ Although typically a server will support only a single Personal
+ Namespace, and a single Other User's Namespace, circumstances exist
+ where there MAY be multiples of these, and a client MUST be prepared
+ for them. If a client is configured such that it is required to
+ create a certain mailbox, there can be circumstances where it is
+ unclear which Personal Namespaces it should create the mailbox in.
+ In these situations a client SHOULD let the user select which
+ namespaces to create the mailbox in.
+
+ Example 5.6:
+ ===========
+
+ < In this example, a server supports 2 Personal Namespaces. In
+ addition to the regular Personal Namespace, the user has an
+ additional personal namespace to allow access to mailboxes in an
+ MH format mailstore. >
+
+ < The client is configured to save a copy of all mail sent by the
+ user into a mailbox called 'Sent Mail'. Furthermore, after a
+ message is deleted from a mailbox, the client is configured to
+ move that message to a mailbox called 'Deleted Items'.>
+
+ < Note that this example demonstrates how some extension flags can
+ be passed to further describe the #mh namespace. >
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")("#mh/" "/" "X-PARAM" ("FLAG1" "FLAG2")))
+ NIL NIL
+ S: A001 OK NAMESPACE command completed
+
+ < It is desired to keep only one copy of sent mail. It is unclear
+ which Personal Namespace the client should use to create the 'Sent
+ Mail' mailbox. The user is prompted to select a namespace and
+ only one 'Sent Mail' mailbox is created. >
+
+ C: A002 CREATE "Sent Mail"
+ S: A002 OK CREATE command completed
+
+ < The client is designed so that it keeps two 'Deleted Items'
+ mailboxes, one for each namespace. >
+
+ C: A003 CREATE "Delete Items"
+ S: A003 OK CREATE command completed
+
+
+
+Gahrns & Newman Standards Track [Page 5]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ C: A004 CREATE "#mh/Deleted Items"
+ S: A004 OK CREATE command completed
+
+ The next level of hierarchy following the Other Users' Namespace
+ prefix SHOULD consist of <username>, where <username> is a user name
+ as per the IMAP4 LOGIN or AUTHENTICATE command.
+
+ A client can construct a LIST command by appending a "%" to the Other
+ Users' Namespace prefix to discover the Personal Namespaces of other
+ users that are available to the currently authenticated user.
+
+ In response to such a LIST command, a server SHOULD NOT return user
+ names that have not granted access to their personal mailboxes to the
+ user in question.
+
+ A server MAY return a LIST response containing only the names of
+ users that have explicitly granted access to the user in question.
+
+ Alternatively, a server MAY return NO to such a LIST command,
+ requiring that a user name be included with the Other Users'
+ Namespace prefix before listing any other user's mailboxes.
+
+ Example 5.7:
+ ===========
+
+ < A server that supports providing a list of other user's
+ mailboxes that are accessible to the currently logged on user. >
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) (("Other Users/" "/")) NIL
+ S: A001 OK NAMESPACE command completed
+
+ C: A002 LIST "" "Other Users/%"
+ S: * LIST () "/" "Other Users/Mike"
+ S: * LIST () "/" "Other Users/Karen"
+ S: * LIST () "/" "Other Users/Matthew"
+ S: * LIST () "/" "Other Users/Tesa"
+ S: A002 OK LIST command completed
+
+ Example 5.8:
+ ===========
+
+ < A server that does not support providing a list of other user's
+ mailboxes that are accessible to the currently logged on user.
+ The mailboxes are listable if the client includes the name of the
+ other user with the Other Users' Namespace prefix. >
+
+
+
+
+
+Gahrns & Newman Standards Track [Page 6]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) (("#Users/" "/")) NIL
+ S: A001 OK NAMESPACE command completed
+
+ < In this example, the currently logged on user has access to the
+ Personal Namespace of user Mike, but the server chose to suppress
+ this information in the LIST response. However, by appending the
+ user name Mike (received through user input) to the Other Users'
+ Namespace prefix, the client is able to get a listing of the
+ personal mailboxes of user Mike. >
+
+ C: A002 LIST "" "#Users/%"
+ S: A002 NO The requested item could not be found.
+
+ C: A003 LIST "" "#Users/Mike/%"
+ S: * LIST () "/" "#Users/Mike/INBOX"
+ S: * LIST () "/" "#Users/Mike/Foo"
+ S: A003 OK LIST command completed.
+
+ A prefix string might not contain a hierarchy delimiter, because
+ in some cases it is not needed as part of the prefix.
+
+ Example 5.9:
+ ===========
+
+ < A server that allows access to the Other Users' Namespace by
+ prefixing the others' mailboxes with a '~' followed by <username>,
+ where <username> is a user name as per the IMAP4 LOGIN or
+ AUTHENTICATE command.>
+
+ C: A001 NAMESPACE
+ S: * NAMESPACE (("" "/")) (("~" "/")) NIL
+ S: A001 OK NAMESPACE command completed
+
+ < List the mailboxes for user mark >
+
+ C: A002 LIST "" "~mark/%"
+ S: * LIST () "/" "~mark/INBOX"
+ S: * LIST () "/" "~mark/foo"
+ S: A002 OK LIST command completed
+
+ Historical convention has been to start all namespaces with the "#"
+ character. Namespaces that include the "#" character are not IMAP
+ URL [IMAP-URL] friendly requiring the "#" character to be represented
+ as %23 when within URLs. As such, server implementers MAY instead
+ consider using namespace prefixes that do not contain the "#"
+ character.
+
+
+
+
+Gahrns & Newman Standards Track [Page 7]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+6. Formal Syntax
+
+ The following syntax specification uses the augmented Backus-Naur
+ Form (BNF) as described in [ABNF].
+
+ atom = <atom>
+ ; <atom> as defined in [RFC-2060]
+
+ Namespace = nil / "(" 1*( "(" string SP (<"> QUOTED_CHAR <"> /
+ nil) *(Namespace_Response_Extension) ")" ) ")"
+
+ Namespace_Command = "NAMESPACE"
+
+ Namespace_Response_Extension = SP string SP "(" string *(SP string)
+ ")"
+
+ Namespace_Response = "*" SP "NAMESPACE" SP Namespace SP Namespace SP
+ Namespace
+
+ ; The first Namespace is the Personal Namespace(s)
+ ; The second Namespace is the Other Users' Namespace(s)
+ ; The third Namespace is the Shared Namespace(s)
+
+ nil = <nil>
+ ; <nil> as defined in [RFC-2060]
+
+ QUOTED_CHAR = <QUOTED_CHAR>
+ ; <QUOTED_CHAR> as defined in [RFC-2060]
+
+ string = <string>
+ ; <string> as defined in [RFC-2060]
+ ; Note that the namespace prefix is to a mailbox and following
+ ; IMAP4 convention, any international string in the NAMESPACE
+ ; response MUST be of modified UTF-7 format as described in
+ ; [RFC-2060].
+
+7. Security Considerations
+
+ In response to a LIST command containing an argument of the Other
+ Users' Namespace prefix, a server SHOULD NOT list users that have not
+ granted list access to their personal mailboxes to the currently
+ authenticated user. Providing such a list, could compromise security
+ by potentially disclosing confidential information of who is located
+ on the server, or providing a starting point of a list of user
+ accounts to attack.
+
+
+
+
+
+
+Gahrns & Newman Standards Track [Page 8]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+8. References
+
+ [RFC-2060], Crispin, M., "Internet Message Access Protocol Version
+ 4rev1", RFC 2060, December 1996.
+
+ [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [ABNF] Crocker, D., Editor, and P. Overell, "Augmented BNF for Syntax
+ Specifications: ABNF", RFC 2234, November 1997.
+
+ [IMAP-URL], Newman, C., "IMAP URL Scheme", RFC 2192, September 1997.
+
+9. Acknowledgments
+
+ Many people have participated in the discussion of IMAP namespaces on
+ the IMAP mailing list. In particular, the authors would like to
+ thank Mark Crispin for many of the concepts relating to the Personal
+ Namespace and accessing the Personal Namespace of other users, Steve
+ Hole for summarizing the two namespace models, John Myers and Jack De
+ Winter for their work in a preceding effort trying to define a
+ standardized personal namespace, and Larry Osterman for his review
+ and collaboration on this document.
+
+11. Authors' Addresses
+
+ Mike Gahrns
+ Microsoft
+ One Microsoft Way
+ Redmond, WA, 98072, USA
+
+ Phone: (425) 936-9833
+ EMail: mikega@microsoft.com
+
+
+ Chris Newman
+ Innosoft International, Inc.
+ 1050 East Garvey Ave. South
+ West Covina, CA, 91790, USA
+
+ EMail: chris.newman@innosoft.com
+
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+Gahrns & Newman Standards Track [Page 9]
+\f
+RFC 2342 IMAP4 Namespace May 1998
+
+
+12. Full Copyright Statement
+
+ Copyright (C) The Internet Society (1998). All Rights Reserved.
+
+ This document and translations of it may be copied and furnished to
+ others, and derivative works that comment on or otherwise explain it
+ or assist in its implementation may be prepared, copied, published
+ and distributed, in whole or in part, without restriction of any
+ kind, provided that the above copyright notice and this paragraph are
+ included on all such copies and derivative works. However, this
+ document itself may not be modified in any way, such as by removing
+ the copyright notice or references to the Internet Society or other
+ Internet organizations, except as needed for the purpose of
+ developing Internet standards in which case the procedures for
+ copyrights defined in the Internet Standards process must be
+ followed, or as required to translate it into languages other than
+ English.
+
+ The limited permissions granted above are perpetual and will not be
+ revoked by the Internet Society or its successors or assigns.
+
+ This document and the information contained herein is provided on an
+ "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+ TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+ BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+ HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+ MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
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