ANT 4 MailChecking is a system-tray utility that lets you know when you have new email messages. It's very easy to set up and use and even includes support for spam filtering. It allows you to set up as many separate accounts as you like and checks for new messages at a regular interval of your choosing.
A tiny window (optionally always-on-top) remains on your desktop, displaying the number of messages waiting for you on your server. You can hide the window, if you prefer, in favor of audio notification. ANT 4 MailChecking also allows you to set up a variety of spam filtering rules, based on sender, subject, and message size. New messages that match any rule you've set up are summarily removed from your server.