What this small tool does, is filters email based on content using key words and phrases set by the user it is filtering mail for,
and determines (or attempts to anyway) whether the email is spam or not. If it is, it optionally labels the mail (in the Subject: line,
it would simply add SPAM: in the front of the subject), or just removes it immediately.
Usage is simple. Basically, in your aliases file (/etc/mail/aliases usually), you add a line like:
username: "|/path/to/spamscan username"
Then run the newaliases command to get it going.
That's basically it. if you are going to run this system wide, you need to set it as the local mailer for your system,
and let it handle all the mail. More on this later.
The only editing you may need to do, is the first few lines of the spamscan program have some configurable parts,
so you'll need to point it to your local mailer, filter directories, etc.