#5.5.0 smtp;550 Recipient address rejected: User unknown in relay recipient table

This message appers once a while about specific users.ANy ideas??
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Your mailserver tried to make a connection to a mailserver to deliver its mail. This connection setup is started by sending a command ('ehlo') to the destination mailserver.
If the mailserver is listening to commands it will answer with a code like 200 Ok, or 550 <error>.
If you want to know what exactly is causing the error you can configure your mail system so that it generates logging.

For Exchange you can do this by entering the Exchange System Manager, go to your outgoing mailserver, open the properties and go to the diagnostics tab (Don't know for sure if it's there, got no Exchange here at the moment).

If you're using some other system like PostFix or QMail look at their respective manuals for the logging. Most of the time this loggin will be in /var/log/qmail or something like that on Linux/Unix.

Perhaps we all started on the wrong foot. What system gives this error message ? How are the clients mailing?

The delivery lookup is on the receiving side.  So the most likely cause is an error there; or maybe the account has been closed.  The only thing you need to check on the sending side is that the address is correct.

Yes if it is indeed about specific e-mail accounts then those accounts no longer exist or more specifically the domain no longer exists.  I would check to make sure that the recepient's domain has a valid MX record.  If the domain doesn't then the SMTP server will kick this error back to you telling you that it is not able to relay the mail message to that user's domain or it is too many hops.  I've had this happen when too many forwards in a person's e-mail is detected and the e-mail is lost in transit.

If you need help locating the MX record reply to this post with just the @domain.com portion of the specific accounts or a sample of them and I'll help you out.
Check this list for the NDR messages for Exchange.


Although this seems to be a Postfix SMTP server looking at the error message.

According to some PostFix help file:
Valid recipient addresses are listed with the relay_recipient_maps parameter. The Postfix SMTP server rejects invalid recipients with "User unknown in relay recipient table". AKA the user doesn't appear to exist on the other side.
ykampAuthor Commented:
Underlying SMTP 500 error.  Our server tried ehlo, the recipient's server did not understand and returned a 550 or 500 error.  Set up SMTP logging.???

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