SMTP Service Extensions (RFC1869)
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
J. Klensin: AUTHOR [+5]
This memo defines a framework for extending the SMTP service by defining a means whereby a server SMTP can inform a client SMTP as to the service extensions it supports. Extensions to the SMTP service are registered with the IANA. This framework does not require modification of existing SMTP clients or servers unless the features of the service extensions are to be requested or provided.
Network Working Group J. Klensin, WG Chair
Request For Comments: 1869 MCI
STD: 10 N. Freed, Editor
Obsoletes: 1651 Innosoft International, Inc.
Category: Standards Track M. Rose
Dover Beach Consulting, Inc.
Network Management Associates, Inc.
SMTP Service Extensions
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.
This memo defines a framework for extending the SMTP service by
defining a means whereby a server SMTP can inform a client SMTP as to
the service extensions it supports. Extensions to the SMTP service
are registered with the IANA. This framework does not require
modification of existing SMTP clients or servers unless the features
of the service extensions are to be requested or provided.
The Simple Mail Transfer Protocol (SMTP)  has provided a stable,
effective basis for the relay function of message transfer agents.
Although a decade old, SMTP has proven remarkably resilient.
Nevertheless, the need for a number of protocol extensions has become
evident. Rather than describing these extensions as separate and
haphazard entities, this document enhances SMTP in a straightforward
fashion that provides a framework in which all future extensions can
be built in a single consistent way.
3. Framework for SMTP Extensions
For the purpose of service extensions to SMTP, SMTP relays a mail
object containing an envelope and a content.
(1) The SMTP envelope is straightforward, and is sent as a
series of SMTP protocol units: it consists of an
originator address (to which error reports should be
directed); a delivery mode (e.g., deliver to recipient
mailboxes); and, one or more recipient addresses.
(2) The SMTP content is sent in the SMTP DATA protocol unit
and has two parts: the headers and the body. The
headers form a collection of field/value pairs
structured according to RFC 822 , whilst the body,
if structured, is defined according to MIME . The
content is textual in nature, expressed using the US
ASCII repertoire (ANSI X3.4-1986). Although e...