SMTP Error Codes

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.

Error	Code	Description

Error	Code	Description
4XX_RVERIFY_DEFER	400	Deferred: temporary directory error
4XX_SUSPECT_REALTIME	420	Deferred due to suspect content, please try again later
4XX_TIMEOUT	421	Error: timeout
4XX_CLIENT_DISCONNECT	421	Client disconnected
4XX_EINTERNAL	421	Internal error
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.
4XX_VIRUSSCAN_TEMP_FAIL	421	Temporary failure. Try again later.
4XX_TEMP_RECIP	450	Requested action not taken: mailbox unavailable.
4XX_EINTERNAL	451	Internal error.
4XX_EINTERNAL	451	Requested action aborted: local error in processing.
4XX_TOO_MANY_RECIPS	452	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.
5XX_INVALID_PARAM	501	Syntax error in parameters or arguments.
5XX_AUTH_ABORT	501	Authentication aborted.
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.
5XX_NO_SUCH_COMMAND	502	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.
5XX_BAD_AUTH_COMMAND_SEQ	503	Bad sequence of authentication commands - Try the following: AUTH CRAM-MD5, AUTH LOGIN.
5XX_BAD_COMMAND_SEQ	503	Bad sequence of commands.
5XX_AUTH_REQUIRES_TLS	504	Error: encryption required for requested authentication mechanism.
5XX_NEED_FQDN	504	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.
5XX_AUTH_REQUIRES_TLS	530	Authentication required.
5XX_REQUIRES_TLS	530	Must issue STARTTLS.
5XX_AUTH_FAILED	535	Authentication failed.
5XX_BLOCKED_RECIP	550	Recipient email address rejected.
5XX_BLOCKED_IP	550	Blocked IP address.
5XX_BLOCKED_SENDER2	550	Sender Rejected.
5XX_BLOCKED_SENDER3	550	Sender email address rejected.
5XX_INVALID_DOMAIN	550	No such domain at this location.
5XX_HANGUP	550	Executing hangup request.
5XX_DISCARD	550	Executing discard request.
5XX_EMPTY_SENDER	550	Empty envelope senders not allowed.
5XX_INVALID_SENDER2	550	Invalid sender address.
5XX_BLOCKED_IP2	550	Sender IP address rejected.
5XX_SPF_FAIL	550	Rejecting for Sender Policy Framework (SPF).
5XX_RECIP 550	550	Requested action not taken: mailbox unavailable.
5XX_SPOOFED	550	Rejecting spoofed message.
5XX_MSG_SIZE	552	Error: message too large.
5XX_MSG_SIZE2	552	Message size exceeds fixed limit.
5XX_FAIL_RECIP	553	Requested action not taken: mailbox name not allowed.
5XX_NO_ACTION	553	Requested action not taken.
5XX_INVALID_RECIP	553	Requested action not taken: mailbox name not allowed.
5XX_FAILED	554	Transaction failed.
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).
5XX_BLOCKED_ATT	554	Rejecting banned file attachment.
5XX_BLOCKED_ATT_ENC	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.