Anti-spam recommendations

[Geoff Shang]

Hello,

I administer a server for a non-profit project.  I need to implement an 
anti-spam solution to cut down on the spam.  It is showing signs of 
getting out of hand and I'd like to put something in place before it does.

I'd like something that doesn't take too much maintaining and hopefully 
doesn't hit too many false-positives.

We're running Debian Lenny with Postfix as our MTA.

Any suggestions welcome.

Cheers,
Geoff.