I have an Exchange 2003 Server (under SBS 2003).
A recipient mailbox needs to forward it's mail out to an external address.
I have used a new AD contact (SMTP address) and Exchange is successfully forwarding internal mail out to the mailbox. However, external mail is not being forwarded. The mail method is an SMTP smarthost so I can't think of any reason it wouldn't send external mail out to what is a completely different domain address.