What's the most annoying thing about e-mail? Spam, of course. There are plenty of spam-killers out there, and MailWasher Pro is a very solid one. It doesn't integrate with your e-mail software; instead, it directly contacts your e-mail server, and will then delete spam so that the spam never reaches your inbox. It flags spam, then lets you delete the spam, or tells the software to let it through because it's not spam. You also have the choice of bouncing the spam back to the sender.
Because it doesn't need to integrate with your e-mail software, it works with virtually any e-mail software. And it's quite configurable. You can create customized filters for determining what's spam, and you create blacklists and whitelists. MailWasher Pro also learns from you, so that it gets smarter over time. In addition, it does basic virus-scanning. You can also read the actual mail itself from within the program, and so it works as a kind of mini e-mail client.