RFC 1204 (rfc1204) - Page 2 of 6

Message Posting Protocol (MPP)

RFC 1204                          MPP                      February 1991


      354 Enter mail, end with .
      451 Local error encountered.
      500 Command unrecognized.
      501 Argument syntax error.
      503 Illegal command sequence.
      530 Authentication Failure.
      550 Error.

2.3.  Command and Reply Descriptions

      USER 

         The USER command informs the message posting server about the
         username of the user trying to submit mail to the network.  The
         required argument for the USER command is a string specifying
         the message sender's username.

         The USER command can only be used under three conditions:

         - when the session with the message posting server has just
           started;

         - right after a message text (terminated by the "."
           sequence) has been successfully submitted to the message
           posting server;

         - right after a USER command that gets the reply code 501.

         List of possible reply codes for the USER command:

         - 250   The username of the message sender has been accepted.

         - 451   Internal error has occurred in the message posting
                 server.

         - 501   Syntax error detected in the username argument.

         - 503   The USER command has been used under an inappropriate
                 condition (i.e., one that is not specified above).

         It is recommended that the message posting server should return
         250 even if the username is not recognized by the message
         posting server, as long as the username is syntactically
         correct.  This is an attempt to prevent the message posting
         server from releasing too much information about the user
         database.  Client should not be able to test the existence of a
         certain username.




Yeh & Lee