SMTP Service Extension for Returning Enhanced Error Codes (RFC2034)
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
This memo defines an extension to the SMTP service [RFC-821, RFC- 1869] whereby an SMTP server augments its responses with the enhanced mail system status codes defined in RFC 1893. These codes can then be used to provide more informative explanations of error conditions, especially in the context of the delivery status notifications format defined in RFC 1894.
Network Working Group N. Freed
Request for Comments: RFC 2034 Innosoft
Category: Standards Track October 1996
SMTP Service Extension for
Returning Enhanced Error Codes
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 an extension to the SMTP service [RFC-821, RFC-
1869] whereby an SMTP server augments its responses with the enhanced
mail system status codes defined in RFC 1893. These codes can then
be used to provide more informative explanations of error conditions,
especially in the context of the delivery status notifications format
defined in RFC 1894.
Although SMTP is widely and robustly deployed, various extensions
have been requested by parts of the Internet community. In
particular, in the modern, international, and multilingual Internet a
need exists to assign codes to specific error conditions that can be
translated into different languages. RFC 1893 defines such a set of
status codes and RFC 1894 defines a mechanism to send such coded
material to users. However, in many cases the agent creating the RFC
1894 delivery status notification is doing so in response to errors
it received from a remote SMTP server.
As such, remote servers need a mechanism for embedding enhanced
status codes in their responses as well as a way to indicate to a
client when they are in fact doing this. This memo uses the SMTP
extension mechanism described in RFC 1869 to define such a mechanism.
3. Framework for the Enhanced Error Statuses Extension
The enhanced error statuses transport extension is laid out as
(1) the name of the SMTP service extension defined here is
(2) the EHLO keyword value associated with the extension is
(3) no parameter is used with the ENHANCEDSTATUSCODES EHLO
(4) the text part of all 2xx, 4xx, and 5xx SMTP responses
other than the initial greeting and any response to
HELO or EHLO are prefaced with a status code as defined
in RFC 1893. This status code is always followed by one
or more spaces.
(5) no additional SMTP verbs are defined by this extension;
(6) the next section specifies how support for the
extension affects the behavior of a server and client
4. The Enhanced-Status-Codes service extension
Servers supporting the Enhanced-Status-Codes extension must preface
the text part of almost all response lines with a status cod...