[mdlug] how did you learn Spam Assassin? (and sendmail?)

[Dean Durant]

Hello, if you are fluent with writing rules, blocking spam, and keeping
the email coming through without many false positives, how did you get
to that point?   Just online resources, and tinkering?   Are there any
books?

The system we have at work is always completely bogged down.   It gets
stuck.   Emails back up, and nothing gets through.   Spamassassin is
installed and seems to work some of the time.   The system also runs
sendmail and clamav.   In particular, I'd like to keep certain hostnames
from even connecting.  I can do a ps -ef | grep sendmail and if some
smtp server in the czech republic or china or wherever is connecting, I
can see it.   I know it is rarely if ever sending legitimate mail.   Can
I tell sendmail to just drop those incoming smtp requests?  
The spam rules don't seem to be working at all.  

The system is a quad cpu or 2 dual core Xeon, 3.0 Ghz, running fedora 7
I think.  
Thanks, Dean