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IMAP4 Compatibility with IMAP2bis (RFC2061)

IP.com Disclosure Number: IPCOM000002612D
Original Publication Date: 1996-Dec-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 3 page(s) / 5K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Crispin: AUTHOR

Abstract

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.

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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.

Introduction

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

1732.

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

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, SU...