Jetzt habe ich mir mal die Zeit genommen das RFC raus zu suchen, in denen die SMTP reject codes definiert sind.
guckst Du hier: rfc2821
.... 4.2.3 Reply Codes in Numeric Order211 System status, or system help reply 214 Help message (Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user) 220 <domain> Service ready 221 <domain> Service closing transmission channel 250 Requested mail action okay, completed 251 User not local; will forward to <forward-path> (See section 3.4) 252 Cannot VRFY user, but will accept message and attempt delivery (See section 3.5.3) 354 Start mail input; end with <CRLF>.<CRLF> 421 <domain> Service not available, closing transmission channel (This may be a reply to any command if the service knows it must shut down) 450 Requested mail action not taken: mailbox unavailable (e.g., mailbox busy) 451 Requested action aborted: local error in processing 452 Requested action not taken: insufficient system storage 500 Syntax error, command unrecognized (This may include errors such as command line too long) 501 Syntax error in parameters or arguments 502 Command not implemented (see section 4.2.4) 503 Bad sequence of commands 504 Command parameter not implemented 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons) 551 User not local; please try <forward-path> (See section 3.4) 552 Requested mail action aborted: exceeded storage allocation 553 Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect) 554 Transaction failed (Or, in the case of a connection-opening response, "No SMTP service here") ....