Choicemail is another for more serious spam blocking.  It's at http://www.digiportal.com/index.html  They have a free version and different paid versions. 

From the web site: 

ChoiceMail is different. It's a permission based spam blocker that customizes itself to you. Permission-based means ChoiceMail assumes email is spam unless it knows otherwise.
Only approved email gets into your inbox. ChoiceMail automatically approves email from people you know and trust. It lets you create simple rules to approve email that is important to you. And it lets you automatically query unknown senders to find out who they are and what they want before their email gets into your inbox. Then you get to decide if this is someone you want to hear from. Legitimate senders respond to this query, but spammers never do.