Is there a possiblity to setup zimbra in a way that only admin can receive all incoming mail. He will then forward only the neccessary mails to particular users. At the same time, all outgoing mails also should come to admin account. He will then forward only the neccessary mails to outside domains. In other words only "admin" can send mails to outside and receive mails from out side. Other users can route mails locally.
This is a unique setup. Therefore very difficult to find howto documents too.