Das Simple Mail Transfer Protocol (SMTP) ist ein Netzwerkprotokoll zur Übertragung von Emails. SMTP-Server melden nach jeder Anfrage einen Statuscode zurück. Diese Codes sind dreistellig. Nach dem dreistelligen Code sendet der Mailserver noch einen beschreibenden Text zur Meldung.
211 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 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 503 Bad sequence of commands 504 Command parameter not implemented 550 Requested action not taken: mailbox unavailable [E.g., mailbox not found, no access] 551 User not local; please try forward-path 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
Quelle: RFC 821