Simple Main Transfer Protocol (SMTP) Status Codes, Extended Simple Mail Transfer Protocol (ESMTP)
In SMTP Status Codes and Extended Simple Mail Transfer Protocol (ESMTP) lesson, you can learn the status codes used by Simple Mail Trasfer Protocol SMTP and Extended Simple Mail Transfer Protocol (ESMTP).
Simple Main Transfer Protocol (SMTP) Status Codes
The following table lists the possible status codes (or commands) exchanged between Simple Mail Transfer Protocol (SMTP) Server and an Simple Mail Transfer Protocol (SMTP) client.
| SMTP Status Codes | Description |
|---|---|
| 211 | Help reply - system status |
| 214 | Help message |
| 220 | Service ready |
| 221 | Closing connection |
| 250 | Requested action okay |
| 251 | User not local - forwarding to <path> |
| 354 | Start mail input |
| 421 | Service not available |
| 450 | Action not taken - mailbox busy |
| 451 | Action aborted - local error |
| 452 | Action not taken - insufficient storage |
| 500 | Command unrecognized or syntax error |
| 501 | Syntax error in parameters or arguments |
| 502 | Command not supported |
| 503 | Bad sequence of commands (given out of order) |
| 504 | Command parameter not supported |
| 550 | Action not taken - mailbox unavailable |
| 551 | Not a local user |
| 552 | Aborted: Exceeded storage allocation |
| 553 | Action not taken - mailbox name not allowed |
| 554 | Transaction failed |
Extended Simple Mail Transfer Protocol (ESMTP)
While using Extended Simple Mail Transfer Protocol (ESMTP) a client who wishes to use the new features initiates the session with the server by issuing an EHLO command, instead of HELO. A compatible server responds with a 250 reply code. This reply is normally multiline, with each line containing a keyword and an optional argument. These keywords specify the SMTP extensions supported by the server. If the server does not support Extended Simple Mail Transfer Protocol (ESMTP), it provides an error (500 Command not recognized) and the sending host reverts back to SMTP. Simple Mail Transfer (SMTP) Service extensions are defined in RFC 1869.
An example for ESMTP command is the SIZE command. SIZE command allows a receiving host to limit the size of incoming messages. The following extensions are normally listed.
250-EXPN - The Expand extension EXPN can be used to request, or expand, a mailing list on the remote server.
250-VERB - The VERB (Verbose) extension will cause the server to work in verbose mode of communication with other server.
250-8BITMIME - The 8BITMIME extension facilitates the exchange of e-mail messages containing octets outside the seven-bit ASCII range.
250-SIZE - The SIZE extension is designed for specifying the maximum size of the message in bytes. The server returns a SIZE extension with a numeric parameter, which will provide decimal specification of the maximum message length to accept (message length includes line terminations, but not the DATA command).
250-DSN - SMTP Service Extension for Delivery Status Notifications.
250-ONEX - One message transaction only
250-ETRN - The ETRN (Extended Turn) extension enables a mail server to request a second mail server to forward outstanding mail messages to it.
In this lesson you have learned Simple Mail Transfer Protocol (SMTP) status codes and Extended Simple Mail Transfer Protocol (ESMTP). Click "Next" to continue.