Any help on this would be so welcome.

We use sendmail to relay mail to 7 other email servers in our domain. We have just switched to a different server and loaded Redhat 8.0 on it. We can send mail just fine. The problem is when some one tries to send a message. It sends a error message back saying "user not known at this site". I think what is happening it is not relaying it to the right domain. It is thinking that is is on the local machine and sends that message out. We are sure it is just one simple setting some where and we have just missed it. Thanks for you help!