Diagnosing Bounced Email

Recently, you may have noticed an increase in the number of “bounced” email messages. This could be partially caused by the upgrade of new anti-spam mechanisms being put into place at many large ISPs and other companies. That is not to say that you shouldn’t”t check your own machine first. But with a little knowledge, you can diagnose where the problem is, simply by reading the ESMTP status codes that are in the returned message.

Example:

PERM_FAILURE: SMTP Error (state 8 ): 554 5.1.0 Sender Denied

This one is easy. The “Sender Denied” text means that the receiving mail server has blocked the sending mail server, or the sender was “blacklisted”. Sometimes it’s not that clear and you need to use the status codes to figure out what happened. The status code in this message is the 554 5.1.0 part. The format is always *** x.x.x, with the x.x.x part being a return code and the *** being an ESMTP status code. Charts of their meanings is below.

In this case it’s easy to see that the message was returned because of an SMTP error. The “Sender Denied” comment on the end means it’s probably because the sending mail server was blacklisted by a spam filter.

x.x.x, Server Return Codes:

The first value indicates the status of the communication between the sender and recipient server. Possible values are:

1	Server accepted the command, but no action taken. Confirmation message is required.
2	Server successfully completed the task.
3	Server understood the request. More information is required to complete.
4	Server encountered a temporary failure on that request. The command may complete if it’s repeated.
5	Server encountered an error.

The second value is an extra level of detail, which indicates the type of error or communication:

0	Syntax error has occured.
1	Message is an informational reply.
2	Message refers to the connection status.
3	Unspecified, may be used for custom messages.
4	Unspecified, may be used for custom messages.
5	Status message refers to the entire mail system or server.

ESMTP Status Codes:

In the event of a failure ESMTP codes can indicate even more detail than server return codes. They can indicate status of either the recipient mail server or your local mail server in response to a problem with your mail client. Possible values are:

211	System status message.
214	Help message formatted for human reader follows.
220	SMTP service ready.
221	Service/connection closing.
250	Successful request. Action completed.
251	Recipient is not local to the server, but the server will accept and forward the message.
252	Recipient can’t be verified, but the server will accept the message and attempt delivery.
354	Start message input now, end with .. Indicates the server is ready to accept a message once you’ve given it From: and To: information
421	Service is not available and connection will be closed.
450	Requested command failed because the recipient’s mailbox is unavailable.
451	Command has been aborted due to a server error. Possibly notify your SysAdmin.
452	Command has been aborted because the server has insufficient system storage.
500	Server could not recognize the command was due to a syntax error. (usually due to mail client error)
501	Syntax error was found in command arguments. (usually due to mail client error)
502	Command was not implemented. (usually due to mail client error)
503	Server has encounterd a bad command or sequence of commands. (usually due to mail client error)
504	Command parameter is not implemented. (usually due to mail client error)
550	Command failed because the user’s mailbox was unavailable (or you did not have permissions to send to this mailbox)
551	Recipient is not local to the server. Server responds with a fowarding address that should be tried.
552	Action was aborted because storage allocation was exceeded.
553	Action was aborted because the mailbox name was invalid.
554	Transaction failed, without a clear reason.