IMAP4 Compatibility with IMAP2bis (RFC2061)
Original Publication Date: 1996-Dec-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
The Internet Message Access Protocol (IMAP) has been through several revisions and variants in its 10-year history. Many of these are either extinct or extremely rare; in particular, several undocumented variants and the variants described in RFC 1064, RFC 1176, and RFC 1203 fall into this category.
Network Working Group M. Crispin
Request for Comments: 2061 University of Washington
Category: Informational December 1996
IMAP4 COMPATIBILITY WITH IMAP2BIS
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
The Internet Message Access Protocol (IMAP) has been through several
revisions and variants in its 10-year history. Many of these are
either extinct or extremely rare; in particular, several undocumented
variants and the variants described in RFC 1064, RFC 1176, and RFC
1203 fall into this category.
One variant, IMAP2bis, is at the time of this writing very common and
has been widely distributed with the Pine mailer. Unfortunately,
there is no definite document describing IMAP2bis. This document is
intended to be read along with RFC 1176 and the most recent IMAP4
specification (RFC 2060) to assist implementors in creating an IMAP4
implementation to interoperate with implementations that conform to
earlier specifications. Nothing in this document is required by the
IMAP4 specification; implementors must decide for themselves whether
they want their implementation to fail if it encounters old software.
At the time of this writing, IMAP4 has been updated from the version
described in RFC 1730. An implementor who wishes to interoperate
with both RFC 1730 and RFC 2060 should refer to both documents.
This information is not complete; it reflects current knowledge of
server and client implementations as well as "folklore" acquired in
the evolution of the protocol. It is NOT a description of how to
interoperate with all variants of IMAP, but rather with the old
variant that is most likely to be encountered. For detailed
information on interoperating with other old variants, refer to RFC
IMAP4 client interoperability with IMAP2bis servers
A quick way to check whether a server implementation supports the
IMAP4 specification is to try the CAPABILITY command. An OK response
will indicate which variant(s) of IMAP4 are supported by the server.
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
The absense of this command indicates IMAP2bis (or older).
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, SU...