RFC 2034 (rfc2034) - Page 3 of 6

SMTP Service Extension for Returning Enhanced Error Codes

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