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Versions: 00 01                                                         
Network Working Group                                      L. Greenfield
Internet Draft                                           Carnegie Mellon
Document: draft-greenfield-acap-mbox-00.txt                  August 1998

                       ACAP Mailbox Dataset Class

Status of this Memo

   This document is an Internet Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
   and its Working Groups.  Note that other groups may also distribute
   working documents as Internet Drafts.

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   A revised version of this draft document will be submitted to the RFC
   editor as a Proposed Standard for the Internet Community.  Discussion
   and suggestions for improvement are requested.  This document will
   expire before January 1999.  Distribution of this draft is unlimited.


   IMAP [IMAP4] allows users to access the mail store in an efficient
   way, but has insufficient support to export detailed meta-level
   information about mailboxes, subscriptions, and multiple servers.
   The mailbox dataset provides a fast, flexible way of exporting this

L. Greenfield                                                   [Page i]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

1.   Conventions Used in this Document

   The key words "MUST", "MUST NOT", "SHOULD" , "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [KEYWORDS].

   The attribute syntax specifications use the Augmented Backus-Naur
   Form (ABNF) notation as specified in [ABNF].

   When UTF-8 [UTF8] is referred to in this document, it refers to
   Unicode version 2.0, and not Unicode version 1.1.

2.   Design Issues

   IMAP [IMAP4] provides a robust protocol for fetching messages and
   partial data from a remote server, both for active and detached
   clients.  However, it provides only rudimentary support for
   determining what mailboxes reside on a server, subscription support,
   and fast updates.  Current proposals for handling mailboxes spread
   over multiple IMAP servers force clients to make complicated and slow

   The mailbox dataset is designed to aid IMAP clients in dealing with a
   large number of mailboxes, possibly spread and replicated over
   multiple servers.  It exports information that cannot be expressed
   via IMAP.

   Clients will be able to use the mailbox dataset to
   * quickly tell what mailboxes have new messages in them
   * receive overview information about the mailbox (statistics and
     mailbox flags)
   * quickly tell what mailboxes have had state changes since they were
     last examined
   * enable "new mailbox" creation messages
   * determine how to "post" messages to this mailbox, if possible
   * present a simple, unified view of a large number of servers

L. Greenfield                                                   [Page 2]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

3.   ACAP/IMAP mail realms

   Large mail sites (both in number of users and amount of mail/news
   processed) require more complex setups than a single IMAP server.  A
   "mail realm" is a collection of ACAP, IMAP, LDAP, and SMTP servers.

   The ACAP server serves to unify the multiple IMAP server into a
   single, coherent form.  Users need not know any details of the
   underlying IMAP servers but are instead presented with simple
   hierarchical names.

   The ACAP mailbox dataset supercedes the IMAP subscription support.  A
   client that uses the ACAP mailbox dataset never sends LIST or LSUB--
   -a superset of that information is available from the ACAP server.

   How a server keeps multiple replicas of a mailbox in sync is not
   addressed by this document.  Any changes to one server MUST be
   reflected in the other servers as soon as possible.

L. Greenfield                                                   [Page 3]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

4.   ACAP Mailrealm Dataset Class

   Datasets whose names begin with "/mailrealm" contain general
   information about this mail realm, as defined in this specification.

           ACAP Attributes

     The name of this mail realm.

     mailrealm-name = 1*TEXT-UTF8-CHAR

     The IMAP servers associated with this mailrealm.

     mailream-imapservers = 1*CHAR *(NUL 1*CHAR)
   ;; multi-valued

     The SMTP server used for posting outgoing mail.  It MAY be sorted
   in order of preferential use.

     mailrealm-smtpservers = 1*CHAR *(NUL 1*CHAR)
   ;; multi-valued

     The LDAP server used for directory information.

     mailrealm-ldapservers = 1*CHAR *(NUL 1*CHAR)
   ;; multi-valued

L. Greenfield                                                   [Page 4]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

5.   ACAP Mailbox Dataset Class

   Datasets whose names begin with "/mailbox" contain mailbox entries as
   defined in this specification.  The hierarchy corresponds to the
   hierarchy defined by the mail realm by the following transformation:

   * change all hierarchy delimiters to "/"
   * change all "\"'s in names to "\\" (if "\" isn't the hierarchy
   * change all "/"'s in names to "\S" (if "/" isn't the hierarchy
   * change the modified UTF-7 encoding to UTF-8

   Any server that provides this dataset should advertise the MAILBOX
   attribute.  Most of the attributes are inherited system wide, though
   some may be overridden on a per-user basis, as defined in [ACAP].

           Required ACAP Attributes

   - Basic Attributes

     The "entry" attribute is the last component in the mailbox.

     The "subdataset" attribute is used to indicate that there are
   submailboxes in the hierarchy from this mailbox.  It's possible the
   mailbox has no real existance on an IMAP server (or exists with the
   \Noselect flag).  In such a case, the "mailbox.Servers" attribute is

   A user MAY still be subscribed to a mailbox with no IMAP server.
   Such a subscription SHOULD be persistant should this mailbox later be
   created, and MAY have meaning to certain clients.  For example, a
   graphical hierarchical client may choose to show a subscribed
   \Noselect mailbox to allow the user quick access to the mailboxes

   - Mailbox Attributes

     This is the name of this mailbox in UTF-8 form, suitable to display
   to a user.
     "comp.mail.imap" or "#news.comp.mail.imap"

     mailbox-name = 1*TEXT-UTF8-CHAR


L. Greenfield                                                   [Page 5]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

     This is the name of this mailbox in modified-UTF7 form, suitable
   for sending to a server as an argument to SELECT.
     "comp.mail.imap" or "#news.comp.mail.imap"

     mailbox-imapname = 1*CHAR

     This is the suggested URL to try to access this mailbox. see

     mailbox-expand-url = URL
                       ;; as defined in [IMAP-URL]

      This is the suggested server to try to access this mailbox.  It
   MUST be listed in "mailbox.Servers".  The server returned SHOULD be
   currently available.

      mailbox-expand-server = 1*CHAR

      This is a list of servers that this mailbox is available on.  If
   there is more than one server, the mailbox MUST be named the same on
   every server and MUST have identical content.  It MAY be sorted in
   preferential order of access.
      ("mail2.andrew.cmu.edu" "mail4.andrew.cmu.edu")

      mailbox-servers = *(NUL 1*CHAR)

      Non-0 if the user is subscribed to this mailbox.  Clients MAY
   support multiple methods of subscription by the following values:
   * 0 unsubscribed
   * 1 normal subscription (show changed messages)
   * 2 show-all subscription (always show all messages)
   * 3 ask subscription (the user needs to take some action to show the
       captions in this mailbox)

   Clients may write to this attribute to change the subscription state;
   mail realms may chose to force this attribute to be non-zero, so that
   users are forced to subscribe to a mailbox containing system

      mailbox-subscribed = number


L. Greenfield                                                   [Page 6]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

      This is the current state of the mailbox, obtained via some
   unspecified method from an appropriate IMAP server.  The IMAP server
   MAY act as an ACAP client and store the appropriate information when
   it changes.

     mailbox-state = number

      This is a URL describing how to post messages to this mailbox.

      mailbox-post = url

      If non-zero, this is considered a repository for a mailing list or
   newsgroup since the time indicated.

      mailbox-archive = time

      This contains an ACAP-format time when this mailbox was created.

      mailbox-createtime = time

      This is a writable attribute containing the IMAP quota of this
   mailbox.  (The exact layout is still under consideration.)

      mailbox-quota = *(quota_resource)
                    ;; multi-valued
      quota_resource = atom SP number SP number

      This is a writable format containing the ACL for this mailbox.
   (The exact layout is still under consideration.)

      mailbox-acl = *(acl_data)
      acl_data = identifier SP acl_rights
      acl_rights = string

L. Greenfield                                                   [Page 7]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

6.   Open Issues

   The author is unsure the best way to encode IMAP ACLs and IMAP QUOTAs
   into the mailbox data set.

   IMAP4 namespaces [NAMESPACE] can lead to many many issues.

   It may be possible to integrate NNTP servers into this proposal; this
   adds even more complexity and could create even more complicated

   The naming scheme for each mailbox (for an N hierarchical name, the
   first N-1 components form the dataset and the last component forms
   the name) feels needlessly complicated.

   Should a more formal definition for server coherency be made?

   Is the mailrealm dataset necessary?

L. Greenfield                                                   [Page 8]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

7.   References

   [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
   ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
   November 1997.

   [ACAP] Newman, Myers, "ACAP -- Application Configuration Access
   Protocol", RFC 2244, Innosoft, Netscape, November 1997.

   [BASIC-URL] Berners-Lee, Masinter, McCahill, "Uniform Resource
   Locators (URL)", RFC 1738, CERN, Xerox Corporation, University of
   Minnesota, December 1994.

   [IMAP4] Crispin, M., "Internet Message Access Protocol - Version
   4rev1", RFC 2060, University of Washington, December 1994.

   [IMAP-ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, Carnegie-
   Mellon University, January 1997.

   [IMAP-QUOTA] Myers, J. "IMAP4 QUOTA extension", RFC 2087, Carnegie-
   Mellon University, January 1997.

   [IMAP-URL] Newman, C. "IMAP URL Scheme", RFC 2192, Innosoft,
   September 1997.

   [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
   Requirement Levels", RFC 2119, Harvard University, March 1997.

   [NAMESPACE] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, Microsoft,
   Innosoft, May 1998.

   [UTF8] Yergeau, "UTF-8, a transformation format of ISO 10646", RFC
   2279, Alis Technologies, January 1998.

8.   Security Considerations

   The mailbox dataset should not export information that would be
   otherwise unavailable to the user.

9.   Author's Address

   Lawrence Greenfield
   Cyert Hall 100c
   Computing Services
   Carnegie Mellon University
   Pittsburgh PA, 15213-3890

L. Greenfield                                                   [Page 9]

Internet DRAFT            ACAP Mailbox Dataset            August 7, 1998

   Email: leg+asg@andrew.cmu.edu

L. Greenfield                                                  [Page 10]