SMTP Service Extension for Authentication (RFC2554)
Original Publication Date: 1999-Mar-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
This document defines an SMTP service extension [ESMTP] whereby an SMTP client may indicate an authentication mechanism to the server, perform an authentication protocol exchange, and optionally negotiate a security layer for subsequent protocol interactions. This extension is a profile of the Simple Authentication and Security Layer [SASL].
Network Working Group J. Myers
Request for Comments: 2554 Netscape Communications
Category: Standards Track March 1999
SMTP Service 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 (1999). All Rights Reserved.
This document defines an SMTP service extension [ESMTP] whereby an
SMTP client may indicate an authentication mechanism to the server,
perform an authentication protocol exchange, and optionally negotiate
a security layer for subsequent protocol interactions. This
extension is a profile of the Simple Authentication and Security
2. Conventions Used in this Document
In examples, "C:" and "S:" indicate lines sent by the client and
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as defined in "Key words for
use in RFCs to Indicate Requirement Levels" [KEYWORDS].
3. The Authentication service extension
(1) the name of the SMTP service extension is "Authentication"
(2) the EHLO keyword value associated with this extension is "AUTH"
(3) The AUTH EHLO keyword contains as a parameter a space separated
list of the names of supported SASL mechanisms.
(4) a new SMTP verb "AUTH" is defined
(5) an optional parameter using the keyword "AUTH" is added to the
MAIL FROM command, and extends the maximum line length of the
MAIL FROM command by 500 characters.
(6) this extension is appropriate for the submission protocol
4. The AUTH command
AUTH mechanism [initial-response]
a string identifying a SASL authentication mechanism.
an optional base64-encoded response
After an AUTH command has successfully completed, no more AUTH
commands may be issued in the same session. After a successful
AUTH command completes, a server MUST reject any further AUTH
commands with a 503 reply.
The AUTH command is not permitted during a mail transaction.
The AUTH command indicates an authentication mechanism to the
server. If the server supports the requested authentication
mechanism, it performs an authentication protocol exchange to
authenticate and identify the user. Optionally, it also
negotiates a security layer for subsequent protocol
interactions. If the requested authentication mechanism is not