I was going to suggest BigHip, but since you evidently want to run your own, for ease of use, you can't go wrong with
ListServ - it's designed more as an email 'collaboration/chat' system, but you can disable all but moderator posts fairly easily.. then just send out your email to
[email protected], or however you want it.
There are many other solutions, but this one will take the least pain and agony on yourself and your administrators.