In Domino 4.X (I'm not sure about 5) there is no obvious way to turn off the ability to send internet e-mail. Although
many companies wish to restrict this. There is a way though, it's a bit tricky but it works great. 1. Set up the SMTP MTA to use short-name as the reply e-mail address. 2. Enter the correct e-mail address for the users that shall be able to send (and receive) internet e-mail. 3. For users that shall not be able to send internet e-mail (Notes mail will still work) enter an e-mail address containing illegal characters such as "????". When a message from this users get to the MTA it will kick the message back telling the sender it contains illegal characters in the header. It pretty straight forward, but needs a bit of administration.