The program connects to your pop server and checks each e-mail to see if it's spam or an address you don't want to get mail from, if it detects such an e-mail you can either delete it, or bounce it back to the sender. Set up your own custom rule lists, a list of friends to always get e-mail from and there is also 12 rules programmed in already that you can turn on and off. Set up as many e-mail accounts as you want.