Receiving E-Mails on my exchange account

I have recently set up and Exchange 2000 server for our company. At the moment I have created users and are able to send messages to other users without any problem.

My problem arises when I try to use external mail. We have a mail server running Eudora Mail and I have tried to do a forwarding from our Eudora Server to each account on the Exchange Server at the moment I can send messages to internet email accounts but cannot receive them.

Any help would be appreciated
Thanks