This is a basic guide to the SMTP return (or 'error') codes you may see for rejected or deferred messages in the Message Log of the Barracuda Email Security Gateway when an outbound message cannot be delivered to or accepted by the destination mail server. Depending on the actual problem it encounters, the destination mail server that did not accept the message may not be able to provide detailed help on how to resolve a problem. In this case the mail server may only provide an SMTP error code in the server's log, or in the text of the message returned to the sender..
To view an SMTP error code for a rejected or deferred message in the Barracuda Email Security Gateway web interface:
- Go to the BASIC > Message Log page.
- Double click on the message.
- In the Delivery Status field you might see Rejected and a Delivery Detail with an SMTP error code. This example shows error 554:
SMTP error codes you'll see in the Delivery Details field of the Message Details popup for a rejected or deferred message include the following, with more details listed in the table below:
- 420 - The message has been deferred due to suspect content. Try again later.
- 421 - The service is not available and the connection will be closed.
- 450 - The requested command failed because the user's mailbox was unavailable (for example because it was locked). Try again later.
- 451 - The command has been aborted due to a server error. Perhaps contact the the administrator to alert him/her of the issue.
- 452 - The command has been aborted because the server has insufficient system storage.
- 454 - TLS encoding is not available due to a temporary condition.
- 500 - The server could not recognize the command due to a syntax error.
- 501 - A syntax error was encountered in command arguments.
- 502 - This command is not implemented.
- 503 - The server has encountered a bad sequence of commands.
- 504 - A command parameter is not implemented.
- 530 - Must issue STARTTLS command.
- 535 - Authentication failed.
- 550 - The requested command failed because the user's mailbox was unavailable (for example, because it was not found, or because the command was rejected for policy reasons).
- 551 - The recipient is not local to the server. The server then gives a forwarding address to try.
- 552 - The action was aborted due to exceeded storage allocation.
- 553 - The command was aborted because the mailbox name is invalid.
- 554 - The transaction failed.
|4XX_RVERIFY_DEFER||400||Deferred: temporary directory error|
|4XX_SUSPECT_REALTIME||420||Deferred due to suspect content, please try again later|
|4XX_ESEND||421||Failed to reply to client|
|4XX_TOO_MANY_ERRORS||421||Too many errors|
|4XX_MSG_PER_SESSION||421||Error: too many messages in one session|
|4XX_TEMP_FAIL||421||Service not available, closing transmission channel. Try again later.|
Temporary failure. Try again later.
|4XX_TEMP_RECIP||450||Requested action not taken: mailbox unavailable.|
|4XX_EINTERNAL||451||Requested action aborted: local error in processing.|
Too many recipients.
|4XX_TLS_TEMP_FAIL||454||TLS not available due to temporary reason.|
|4XX_BLOCKED_RATE||454||Too many connections from origin (rate control).|
|4XX_BLOCKED_RATE2||454||Too many connections to server (rate control).|
|4XX_SYNTAX_ERROR||500||Syntax error, command unrecognized.|
|5XX_INVALID_CHAR_RECIP||500||Syntax error - invalid character.|
Syntax error in parameters or arguments.
|5XX_AUTH_MALFORMED||501||Malformed authentication input.|
|5XX_AUTH_RESPONSE_BAD||501||Error: malformed authentication response.|
|5XX_DATA_LINE_TOO_LONG||501||Command line too long or no terminating CRLF in line buffer .|
|5XX_DATA_MISSING_CRLF||501||No terminating CRLF in line buffer.|
This command is not implemented.
|5XX_MISSING_EHLO||503||Error: send HELO/EHLO first.|
|5XX_ALREADY_AUTH||503||Error: already authenticated.|
|5XX_AUTH_REQUIRES_TLS||503||Issue STARTTLS first before using clear text password.|
Bad sequence of authentication commands - Try the following: AUTH CRAM-MD5, AUTH LOGIN.
Bad sequence of commands.
|5XX_AUTH_REQUIRES_TLS||504||Error: encryption required for requested authentication mechanism.|
Need Fully Qualified Address (FQDN).
|5XX_ERROR_PARAM||504||Command parameter not implemented.|
|5XX_AUTH_UNSUPPORTED||504||Error: unsupported mechanism.|
|5XX_AUTH_TYPE||504||Unrecognized authentication type.|
Must issue STARTTLS.
|5XX_BLOCKED_RECIP||550||Recipient email address rejected.|
|5XX_BLOCKED_IP||550||Blocked IP address.|
|550||Sender email address rejected.|
No such domain at this location.
|5XX_HANGUP||550||Executing hangup request.|
|5XX_DISCARD||550||Executing discard request.|
Empty envelope senders not allowed.
|5XX_INVALID_SENDER2||550||Invalid sender address.|
|5XX_BLOCKED_IP2||550||Sender IP address rejected.|
Rejecting for Sender Policy Framework (SPF).
|5XX_RECIP 550||550||Requested action not taken: mailbox unavailable.|
|550||Rejecting spoofed message.|
Error: message too large.
|5XX_MSG_SIZE2||552||Message size exceeds fixed limit.|
Requested action not taken: mailbox name not allowed.
|553||Requested action not taken.|
|5XX_INVALID_RECIP||553||Requested action not taken: mailbox name not allowed.|
|5XX_BLOCKED_VIRUS||554||Rejected due to virus.|
|5XX_BLOCKED_SPAM||554||Rejected due to spam content.|
|5XX_BLOCKED_NO_PTR||554||IP name lookup failed. No PTR record found for the given IP address.|
|5XX_BLOCKED_RBL||554||Service unavailable; client host blocked. The final sending domain or IP address may be on a Real Time Blocklist (RBL).|
|554||Rejecting banned file attachment.|
|554||Rejecting password protected file attachment.|
|5XX_BLOCKED_BBL||554||Service unavailable; client host [IP or hostname] blocked using Barracuda Reputation; http://www.barracudanetworks.com/reputation/|
|5XX_BLOCKED_DLP||554||Rejected due to banned content.|
|5XX_BLOCKED_SPAM2||554||Rejected due to banned content.|