On our server we are using policyd 1.x together with Postfix 2.1.5 for greylisting and enforcing incoming quotas from unauthorized users (ie. mail for our domains). For this, I have set up Postfix ...
I think this is one area that is a pain for every sysadmin. Users don't really know how much storage space they are using, and don't take the time to manage what is stored there, or how long it stays ...