We have exchange 2000 server set up

[TwitchyTheTramp]

We have exchange 2000 server set up on one of our sites to handle its mail. Everything has seemed fine until one of our customers pointed out a problem we are having. The scenario is as follows: The customer sent an email to somebody in their own company as the To line. In the CC line they put the address of somebody in our company. Everybody receives the intended message fine, in our company and our customer's, BUT the customer then receives a non-deliverable mail message from OUR postmaster automatically saying the address they put in the To line (ie. addressed to somebody within their company) could not be delivered within ours. How do we stop this behaviour?

Thanks in advance for any replies,

Nick

 

[TwitchyTheTramp]

Oops sorry people, I forgot to add a subject.

Nick