IMAP4 Binary Content Extension (RFC3516)
Original Publication Date: 2003-Apr-01
Included in the Prior Art Database: 2003-Apr-17
Internet Society Requests For Comment (RFCs)
This memo defines the Binary extension to the Internet Message Access Protocol (IMAP4). It provides a mechanism for IMAP4 clients and servers to exchange message body data without using a MIME content- transfer-encoding.
Network Working Group L. Nerenberg
Request for Comments: 3516 Orthanc Systems
Category: Standards Track April 2003
IMAP4 Binary Content Extension
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 (C) The Internet Society (2003). All Rights Reserved.
This memo defines the Binary extension to the Internet Message Access
Protocol (IMAP4). It provides a mechanism for IMAP4 clients and
servers to exchange message body data without using a MIME content-
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 described in [KEYWORD].
The abbreviation "CTE" means content-transfer-encoding.
The MIME extensions to Internet messaging allow for the transmission
of non-textual (binary) message content [MIME-IMB]. Since the
traditional transports for messaging are not always capable of
passing binary data transparently, MIME provides encoding schemes
that allow binary content to be transmitted over transports that are
not otherwise able to do so.
The overhead of MIME-encoding this content can be considerable in
some contexts (e.g., slow radio links, streaming multimedia).
Reducing the overhead associated with CTE schemes such as base64
Nerenberg Standards Track [Page 1]
RFC 3516 IMAP4 Binary Content Extension April 2003
can give a noticeable reduction in resource consumption. The Binary
extension lets the server perform CTE decoding prior to transmitting
message data to the client.
3. Content-Transfer-Encoding Considerations
Every IMAP4 body section has a MIME content-transfer-encoding.
(Those without an explicit Content-Transfer-Encoding header are
implicitly labeled as "7bit" content.) In the terminology of [MIME-
IMB], the CTE specifies both a decoding algorithm and the domain of
the decoded data. In this memo, "decoding" refers to the CTE
decoding step described in [MIME-IMB].
Certain CTEs use an identity encoding transformation. For these CTEs
there is no decoding required, however the domain of the underlying
data may not be expressible in the IMAP4 protocol (e.g., MIME