| Value | Meaning |
|---|---|
| HELP_STATUS211 | |
| HELP214 | |
| READY220 | |
| QUIT221 | |
| AUTH_SUCCESS235 | |
| OK250 | |
| FORWARD251 | |
| VRFY_FAIL252 | |
| AUTH_CONTINUE334 | |
| DATA_START354 | |
| NA421 | |
| NEED_PASSWORD435 | |
| BUSY450 | |
| ABORTED451 | |
| STORAGE452 | |
| TLS454 | |
| SYNTAX500 | |
| SYNTAX_PARAM501 | |
| NI502 | |
| BAD_SEQUENCE503 | |
| NI_PARAM504 | |
| AUTH_REQUIRED530 | |
| AUTH_TOO_WEAK534 | |
| AUTH_CRED535 | |
| AUTH_ENCRYPTION538 | |
| MAILBOX550 | |
| TRY_FORWARD551 | |
| MAILBOX_STORAGE552 | |
| MAILBOX_NAME553 | |
| FAIL554 |
SMTP server reply codes, RFC 2921, April 2001