[Mimedefang] Limiting access to "everybody" alias

[Kenneth Porter]

I'd like to provide an "all hands" alias for my office so that company 
officers can send out announcements. MD seems like it would be a good place 
to lock down this alias to keep others from abusing it. Does anyone have a 
good recipe for implementing this kind of limitation?

I have a similar requirement for my online game team, which plays numerous 
games. I have an alias for each game that goes to the list of players 
involved with that game, and I don't want spammers abusing these addresses.