I agree with the others, I've never gotten spam from or via avast or its forums. Sorry, one exception, if I remember correctly; a year or two ago a new "member" here was spamming others very briefly, but vlk and others at alwil quickly took care of both that individual and improvements to their security setup here.
I've only got 2 email addys, my "main" one (which is what I use just about everywhere) on my ISP's POP server and one at Yahoo which is essentially a backup. My ISP's own "SpamGuard" service (they use the name generically since they've switched service providers a few times over the years) is excellent at filtering and quarantining stuff, and I might get all of two or three messages a month slip past that. And for those, I simply tell Thunderbird to treat them as junk.
There's almost no mail at the Yahoo addy, since I don't normally give that out, and Yahoo's so far been 100% effective at catching the rare (1 or 2 a day) spam that goes there.
So I don't bother with MailWasher or the like, I feel that I'm getting excellent protection from outside.