I have a customer in Austria, they have recently changed their MX records to a new IP address. I can send them emails which they receive no problem, when they send me an email, I don't receive it. They send over 20,000 emails a week to other countries all over the world, including our own, and we seem to be the only ones having a problem, I have run message tracking in Exchange, but it does not find any emails from this domain. I can telnet onto their mail server and send an email to our Exchange server and we receive it. Please help?