If you are fed up of getting spam emails, then SpamSieve is a very good option. It has just been updated to version 2.7.
The new version includes the following changes;
* Now requires Mac OS X 10.4 or later.
* Made a variety of accuracy improvements, focused on dealing with obfuscations, image attachments, URLs, and HTML.
* Improved corpus speed and memory use.
* Made various improvements to the column widths and alignment in the rules and corpus windows, and added alternating row colors.
* Fixed a rare problem where Apple Mail on Mac OS X 10.5 might hang if you trained a message as spam while Mail was downloading messages.
* Improved sorting of sound names in the pop-up menu.
* Updated the Dutch localization.
All this plus much more.