I have 2 email domains both have their own server. I want to use Exchange solely for an address book for all my Outlook clients. I don't have a problem sending email properly between these domains. However when my clients send an email to an outside domain they get the exchange domain attached to the email. Which is not what we want. I can set the reply to address, but the problem then becomes if a user sends and email internally, it stays local to the exchange server and doesn't send the mail to the proper domain. Anyway to get this accomplished?

I'm not sure if I understand correctly but If I were you I would look at your user at Active Directory.

Look at E-mail Addresses and see wichd domain appears at SMTP. Probably there's something like xxx@yourdomain.local. Change it to xxx@yourdomain.com (if applyes).