Exchange domain e-mail

My Exchange 2007 server is using the users’ domain as their email address. For example, if my domain were “foo.bar.edu,” the address coming up in Exchange is “user@foo.bar.edu.” I only want the address to be “user@bar.edu.” I’ve manually changed their SMTP e-mail addresses to reflect that, but in the Outlook Address Book, their e-mail addresses are still populated as “user@foo.bar.edu.” How do I change this?