RFC 2034 (rfc2034) - Page 3 of 6
SMTP Service Extension for Returning Enhanced Error Codes
Alternative Format: Original Text Document
RFC 2034 SMTP Enhanced Error Codes October 1996
When responses are continued across multiple lines the same status
code must appear at the beginning of the text in each line of the
response.
Servers supporting this extension must attach enhanced status codes
to their responses regardless of whether or not EHLO is employed by
the client.
5. Status Codes and Negotiation
This specification does not provide a means for clients to request
that status codes be returned or that they not be returned; a
compliant server includes these codes in the responses it sends
regardless of whether or not the client expects them. This is
somewhat different from most other SMTP extensions, where generally
speaking a client must specifically make a request before the
extended server behaves any differently than an unextended server.
The omission of client negotiation in this case is entirely
intentional: Given the generally poor state of SMTP server error code
implementation it is felt that any step taken towards more
comprehensible error codes is something that all clients, extended or
not, should benefit from.
IMPORTANT NOTE: The use of this approach in this extension should be
seen as a very special case. It MUST NOT be taken as a license for
future SMTP extensions to dramatically change the nature of SMTP
client-server interaction without proper announcement from the server
and a corresponding enabling command from the client.
6. Usage Example
The following dialogue illustrates the use of enhanced status codes
by a server:
S:
C:
S: 220 dbc.mtview.ca.us SMTP service ready
C: EHLO ymir.claremont.edu
S: 250-dbc.mtview.ca.us says hello
S: 250 ENHANCEDSTATUSCODES
C: MAIL FROM:[email protected]>
S: 250 2.1.0 Originator [email protected]> ok
C: RCPT TO:[email protected]>
S: 250 2.1.5 Recipient [email protected]> ok
C: RCPT TO:[email protected]>
S: 550 5.1.1 Mailbox "nosuchuser" does not exist
C: RCPT TO:[email protected]>
S: 551-5.7.1 Forwarding to remote hosts disabled
Freed Standards Track