[rt-users] filtering user creation on emails

[Sean Perry]

Is there a good place to drop a filter that prevents new user additions 
if they do not match some regex?  In particular we have the auto-cc 
feature enabled, which is quite nice.  But every now and then someone 
accidently leaves in a cc to some address we dont want in the system 
(mailing list, outside addy, etc).  Since I can not delete bad accounts 
I have to look at the User list periodically and lock them.