Linux with Active Directory authentication - how to automatically forward user's mail
I have Linux servers set up to authenticate users from AD. Say user "joe" logs in, then a Unix user "joe" is created. When that user receives mail, it goes into his system mailbox. How can I configure my system so that when "joe" gets email, the mail is automatically forwarded to his email "email@example.com" ? I've looked at a few tutorials, and they require putting the specific user and their forwarding address in /etc/aliases. Is there a way to have the system automatically check if the user is an AD user, then send it to their correct email?
I'm using Centos 5.3, with Samba/winbind authentication against Active Directory, and procmail. I can use any other mail agent if necessary.