SMTP Response Codes

March 26, 2020 Contributors

SMTP Response Codes

The SMTP response codes and their meanings are shown in the following table.


Prior to versions 3.1 and, Momentum would not respond correctly to a 251 (User not local; Will be forwarded) response from a remote server. It put the message in the delayed queue.

Code Meaning
211 System status, or system help reply
214 Help message
220 service ready
221 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 .
421 service not available, closing transmission channel
450 Requested mail action not taken: mailbox unavailable
451 Requested action aborted: error in processing
452 Requested action not taken: insufficient system storage
500 Syntax error, command unrecognized
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
551 User not local; please try
552 Requested mail action aborted: exceeded storage allocation
553 Requested action not taken: mailbox name not allowed
554 Transaction failed