RFC 2034 (rfc2034) - Page 2 of 6
SMTP Service Extension for Returning Enhanced Error Codes
Alternative Format: Original Text Document
RFC 2034 SMTP Enhanced Error Codes October 1996
3. Framework for the Enhanced Error Statuses Extension
The enhanced error statuses transport extension is laid out as
follows:
(1) the name of the SMTP service extension defined here is
Enhanced-Status-Codes;
(2) the EHLO keyword value associated with the extension is
ENHANCEDSTATUSCODES;
(3) no parameter is used with the ENHANCEDSTATUSCODES EHLO
keyword;
(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;
and,
(6) the next section specifies how support for the
extension affects the behavior of a server and client
SMTP.
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 code. As in
RFC 1893, the syntax of these status codes is given by the ABNF:
status-code ::= class "." subject "." detail
class ::= "2" / "4" / "5"
subject ::= 1*3digit
detail ::= 1*3digit
These codes must appear in all 2xx, 4xx, and 5xx response lines other
than initial greeting and any response to HELO or EHLO. Note that 3xx
responses are NOT included in this list.
All status codes returned by the server must agree with the primary
response code, that is, a 2xx response must incorporate a 2.X.X code,
a 4xx response must incorporate a 4.X.X code, and a 5xx response must
incorporate a 5.X.X code.
Freed Standards Track