Two days ago we started to be unable to email anyone with an optonline.net email address.
We are running Exchange 2000 and Server 2000.
The only thing that has changed in the system is that I have installed Exchange Standard 2003 on Exchange 2003 Server in anticipation of upgrading. Only one mailbox has been moved.
This is the error message I receive
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<exchange.dss.com #5.5.0 smtp;550 <firstname.lastname@example.org>: Recipient address rejected: User unknown in relay recipient table>
I did an nslookup and it returned a valid record for optonline.net