My oldest and longest running email account got on a bad spammer list a couple of years ago. Has pretty much rendered it useless.
I was agonizing over just shutting it down for good which made me sad.
Decided to try one last thing before I gave up.
SpamSieve,
SpamSieve: Easy-to-use Mac spam filter for Apple Mail, Outlook, Entourage, Postbox, and more
They have a free one month fully functioning demo. Only took about 3 hours to decide it will be worth the $30 for the paid app.
If you're on a Mac and spam is killing you I highly recommend it.