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.
This was first published in November 2000