A simple PHP script which will monitor your mailboxes and display nearly real-time information about your users' POP mail inboxes, including sizes, last access times, and more in an easy-to-read-at-a-glance web based interface.
PoCoMy: Postfix + Courier + Mysql :: Webfrontend for administration. Features: Virtual domains, forwarding, aliases, sender aliases, multi user, multi language, privileges system, delegation of rights per domain, ...
A daemon that provides a method to track generic POP3 or IMAP logins and then email (in future:also block) the user if they exceed the number of accesses per given minutes allowed.