I am running Exchange 5.5 in an NT 4.0 domain. I want to forward a user's mail to another Exchange server outside my domain. How can I do that? I have POP enabled.
Basically, this process entails creating a custom recipient and modifying the delivery options for the mailbox whose mail you wish to forward.
For step-by-step instructions on how to do this, have a look at Microsoft Knowledge Base article 255697 - XADM: How to Forward E-mail Messages from an Exchange Mailbox to a POP3 Address.