RFC 2061 (rfc2061) - Page 2 of 3

IMAP4 Compatibility with IMAP2bis

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RFC 2061                  IMAP4 Compatibility              December 1996


   If the client does not find any of its known variant in the response,
   it should treat the server as IMAP2bis.  A BAD response indicates an
   IMAP2bis or older server.

   Most IMAP4 facilities are in IMAP2bis.  The following exceptions
   exist:

   CAPABILITY command
            The absense of this command indicates IMAP2bis (or older).

   AUTHENTICATE command.
            Use the LOGIN command.

   LSUB, SUBSCRIBE, and UNSUBSCRIBE commands
            No direct functional equivalent.  IMAP2bis had a concept
            called "bboards" which is not in IMAP4.  RFC 1176 supported
            these with the BBOARD and FIND BBOARDS commands.  IMAP2bis
            augmented these with the FIND ALL.BBOARDS, SUBSCRIBE BBOARD,
            and UNSUBSCRIBE BBOARD commands.  It is recommended that
            none of these commands be implemented in new software,
            including servers that support old clients.

   LIST command
            Use the command FIND ALL.MAILBOXES, which has a similar syn-
            tax and response to the FIND MAILBOXES command described in
            RFC 1176.  The FIND MAILBOXES command is unlikely to produce
            useful information.

   * in a sequence
            Use the number of messages in the mailbox from the EXISTS
            unsolicited response.

   SEARCH extensions (character set, additional criteria)
            Reformulate the search request using only the RFC 1176 syn-
            tax.  This may entail doing multiple searches to achieve the
            desired results.

   BODYSTRUCTURE fetch data item
            Use the non-extensible BODY data item.

   body sections HEADER, TEXT, MIME, HEADER.FIELDS, HEADER.FIELDS.NOT
            Use body section numbers only.

   BODY.PEEK[section]
            Use BODY[section] and manually clear the \Seen flag as
            necessary.





Crispin                      Informational
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