With Exchange 5.5, how do I block a particular user from sending/receiving e-mail to/from the Internet?
The easiest way to prevent someone from receiving Internet e-mail is to give them an invalid SMTP address (or no SMTP address at all).
To prevent them from sending e-mail to the Internet, you need to modify permissions on the Internet Mail Service (IMS). Do this in Exchange Administrator (IMS Properties, Delivery Restrictions, then stop and restart the IMS). If someone's mailbox is denied permission to use the IMS, then they cannot send messages to the Internet (at least not through the IMS).
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