[Exim] Spam Filtering Language

I'm looking for some spam filtering examples and some exim language
help. What I want to do is to conatenate string StrA = StrB + StrC.
Specifically, I want to add the subject line to the first and last 500
characters of the body and test the resulting string for phrases to
filter.

Anyone got and good spam filter code to post? Or other suggestions as to
what works best?