ChoiceMail One Description:

"Now supporting AOL, MSN, Hotmail and Yahoo, as well as POP3 systems, ChoiceMail is a spam-blocking system based on the premise that all incoming email is assumed to be spam until senders have obtained permission (called registering) to send you email. Until they do so, mail from unapproved senders will not appear in your email application. Unapproved senders are automatically offered the opportunity to register. If they do so you are notified so that you can choose to approve (or not) all future emails from that sender. You can also easily preapprove your existing contacts. The registration process requires manual intervention by the sender, thereby eliminating all automatic spamming systems. When our system tray icon flashes, you've got legitimate mail."