SMTP Service Extensions for Transmission of Large and Binary MIME Messages (RFC1830)
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
This memo defines two extensions to the SMTP service. The first service enables a SMTP client and server to negotiate the use of an alternate DATA command "BDAT" for efficiently sending large MIME messages. The second extension takes advantage of the BDAT command to permit the negotiated sending of unencoded binary data.
Network Working Group G. Vaudreuil
Request for Comments: 1830 Octel Network Services
Category: Experimental August 1995
SMTP Service Extensions
for Transmission of Large
and Binary MIME Messages
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
This memo defines two extensions to the SMTP service. The first
service enables a SMTP client and server to negotiate the use of an
alternate DATA command "BDAT" for efficiently sending large MIME
messages. The second extension takes advantage of the BDAT command
to permit the negotiated sending of unencoded binary data.
The MIME extensions to the Internet message protocol provides for the
transmission of many kinds of data which were previously unsupported
in Internet mail. Anticipating the need to more efficiently
transport the new media made possible with MIME, the SMTP protocol
has been extended to provide transport for new message types. RFC
1426 defines one such extension for the transmission of unencoded 8
bit MIME messages [8BIT]. This service extension permits the
receiver SMTP to declare support for 8 bit body parts and the sender
to request 8 bit transmission of a particular message.
One expected result of the use of MIME is that the Internet mail
system will be expected to carry very large mail messages. In such
transactions, there is a need to eliminate the requirement that the
message be scanned for "CR LF . CR LF" sequences upon sending and
receiving to detect the end of message.
Independent of the need to send large messages, Internet mail is
increasingly multi-media there is a need to avoid the overhead of
base64 and quoted-printable encoding of binary objects sent using the
MIME message format over SMTP between hosts which support binary
This memo uses the mechanism defined in [ESMTP] to define two
extensions to the SMTP service whereby a client ("sender-SMTP") may
declare support for the message chunking transmission mode using the
BDAT command and support for the sending of Binary messages.
3. Framework for the Large Message Extensions
The following service extension is hereby defined:
1) The name of the data chunking service extension is
2) The EHLO keyword value associated with this extension is
3) A new SMTP verb is defined "BDAT" as an alternative to
the "DATA" command of [RFC821]. The BDAT verb takes two
arguments. The first argument indicates the length of the
binary data packet. The second optional argument in...