new to filtering...

I have two class Cs that are hammering my mail server regularly. I would like to reject all traffic from these IP ranges. Can someone give me some instruction on how to do this? For example, these two class Cs: 84.243.200, 84.243.199 ?

* What's the command to block all traffic from those IPs?
* How can I view logs showing blocked activity?
* What FreeBSD versions support the filtering system and is this built in by default or have to be installed?
* Is there a tutorial on IPF available online?

Thanks for any help!
See this loosely related thread. There are some resources there to get you started with pf.

I'm not a mailserver guy, but isn't there some access control mechanism at the application level you can utilize? (At least until you get your packet filtering ruleset into place...)