Preventing and tailoring users’ email

We have a number of users who are taking liberties with their external email and management have asked us to disable their rights for external emailing.

Firstly, what is the best way to do this (we use Exchange 5.5) and secondly, if we do allow rights for certain users, is there a way of having a copy of their outgoing messages sent automatically to a manager’s mailbox for monitoring purposes (as they would like it would be as automatic a process as possible).

Thanks in advance.