We have a domain we use for email abc.com.We have a main directory (which is employees) and we have a secondary address book (directory assistance) which is external users (not employees) where usernames and email addresses are stored. If I email an employee user@abc.com it works fine. If I email a user from secondary address book at user@companydomain.com, that works. The issue is, I can email the external user @abc.com also, and it will forward to the email address in the secondary address book. How can I prevent this from happening?