Mail periodically freezes

Ever since I upgraded SpamSieve to 2.8.3, my Apple Mail client will periodically (once or twice a day) stop loading mail from any of my (4) mail servers. I quit Mail and re-start it and SpamSieve will re-start and filter out all the junk I had received. It’s as if SpamSieve is choking on a message and blocking anything from getting to my Spam folder or my In Box.

The only changes to my system have been the SpamSieve upgrade to 2.8.3 and the new Apple graphics drivers.

I don’t think there were any changes to SpamSieve that would cause this. However, if you want to find out what Mail is doing, you could open the Activity Monitor program and select Mail in the list. When it gets stuck downloading, choose Sample Process from the View menu. Then save the resulting data to a file and send it to me via e-mail.

Clarification
I should mention that, other than not delivering mail, the Mail client remains fully responsive. The menus all work, I can read messages, etc.