We had a player do that a few years ago.  Spammed a crapload of forums with adverts.  I just said "Hey don't do that".  And she said "'kay".  The reaction from some of the people on the forums was far more exuberant than what she did.  

Well you could do anything you wanted to your players on your game.  But don't a lot of mud admins attempt to exercise enough control already over their players behavior already?   Well that's rhetorical.  I wouldn't bother.