Do you wanna know the best spam filter I found?
http://www.spamihilator.com/
It's free and works great here. Honestly, give it a try.. it's quite small and will surprise you, I thought even better than MailWasher.
It works with any email program 'cause it works like a proxy for your pop account. When you check your email only the real emails will go thru. You can later open the software and teach him what's spam and what's not, and if it filtered any real emails as spam accidentally you can just recover them with one button. It works.
