server admn help

[RoboticGolem]

I run a small mail server mainly for friends and I and I'm having a
problem.  Every week or so someone, from a different IP every time,
tries to bust into my server.  From my experience with linux I dont
see why this cant be done, I just dont know where to start.

Is there any way to have the system black list ips that fail a login
attempt 2 or 3 times and have it automatically blacklist people who
try users that dont exist?

...or if you could point me to a webpage that discusses this that
would be great.

Thanks in advance,
Matt