I am running Postfix / Dovecot on my email server and I was wondering what is the best way to make sure people are not going over board on their email. I was wanting to create some kind of limit or cap on user mailboxes so they don't utilize more than necessary disk space. Right now my /home directory is ~100GB and everyones email is stored in ~/Maildir/. Can anyone please tell me what they recommend I do? Right now only 30% of home is being utilized however I would like something in place and not need it rather than to find out my email server stopped receiving email because of one user in particular.

I host about ~220 mailboxes on my email server.