I have been having gradually worsening major issues with the handling of junk mail.
I've said it once and I've said it again.
Spam filtering at client level is a waste of time.
By the time the spam reaches your computer, its too late, you've lost many upstream filtering opportunities and techniques that you can't employ at client level. You've also just wasted your bandwidth downloading the junk and your CPU capacity analysing it.
The false positive risk is also a lot higher with client side filtering, and the miss-rate is also higher.
Talk to your mail host about spam filtering services they offer. If they don't offer any, consider changing mail host to one that does.