[exim] Anti SPAM Exim configuration

I manage to filter nearly 100% of spam. I could go into a lot of detail
about how I do that but here's the highlights.

First - I use the Exim ACL tricks that many people have published here.
The best ones include:

Sender Callback Verification
Spamhaus Blacklist
No IP address in HELO
No pretending they are one of my domains in HELO
I nuke all viruses and windows executable attachments.

This gets rid of 90% + of spam

Then - I use Spam Assassin for the rest of it. But - the ACLs get rid of
more spam that Spam Assassin does.

I also do front end spam filtering for other people's domains - so if
you don't want to figure it all out yourself you can route your email
through my servers (for a small price) and I'll clean the spam for you.