Non conosco Exchange ma ho trovato questo:

5.3 Q: How can I prevent a user from sending and receiving Internet mail?

A: Follow the steps outlined below:

Create a group called InternalOnly.

Create a recipient policy that gives them a fake SMTP address. i.e. @fake.domain. Leave the X400 address alone so they can receive internal mail.

Drill down through Routing Groups > Group Name > Connectors > SMTP internet connector(s), choose its properties. Choose the Delivery Restrictions tab, and under "reject", add this group. Do this for each connector.

Follow the steps in Q277872, regarding Connector Restrictions.
[Now they can't use the SMTP connector(s) to send external mail]


Da: http://www.swinc.com/resource/e2kfaq_sec5.htm