I wrote this up for my customers, but I think I'll share it with all of
you who want to make your spam filtering better. Most of the spam on my
system is rejected by EXIM rules with Spam Assassin getting only 10% of
the messages.
http://www.ctyme.com/hosting/how-spam-filter-works.htm
It gives an overview of my entire system for filtering spam. Doesn't
contain any code - but is more of the system structure. I think a lot of
you might find this interesting. I'm always looking for more tricks as
I'm sure most of you are too.