List of SMTP response and error codes
The SMTP protocol (Simple Mail Transfer Protocol) is a standard for sending E-mail messages. The SMTP protocol cannot be used for receiving. The IETF (Internet Engineering Task Force) keeps the standard in document RFC 5321.
SMTP is a challenge-response type protocol. Meaning that the client sends a challenge and the server responds. A response always starts with a 3 digit code which contains the general meaning of the response.
The first digit of an SMTP server response determines the response category:
- 2xx (Success): The action was successful.
- 3xx (Additional data required): Need more information.
- 4xx (Transient Error): The action was unsuccessful but it makes sense to try again later.
- 5xx (Permanent Error): The action was unsuccessful and it does not make sense to try again.
200 – Success codes
|211||System status, or system help reply|
|214||Help/Info message; Intended for the human user|
|221||Service closing transmission channel|
|250||Requested mail action completed|
|251||User not local; message will be forwarded|
|252||Cannot verify user, but will accept message and attempt delivery|
300 – Additional data required
|354||Start mail input; The server expects the e-mail body|
400 – Transient errors
|421||Service not available, closing transmission channel; When the server is shutting down|
|450||Requested mail action not taken: mailbox unavailable (e.g., mailbox busy or temporarily blocked for policy reasons)|
|451||Requested action aborted: error in processing|
|452||Requested action not taken: insufficient system storage|
|455||Server unable to accommodate parameters|
500 – Permanent errors
|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, or command rejected for policy reasons)|
|551||User not local; The server will not forward|
|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”)|
|555||MAIL FROM/RCPT TO parameters not recognized or not implemented|