The amount of spam I get through my business account, which is exposed to spambots, is fairly small, about 37 spam a day. The amount of spam I get through my personal account, which is hidden yet visible in a clever way, is far less, at most 6 each day. This totals to about 35 to 45 spam a day that I have to ignore. My mail traffic is small enough that I can generally deal with this through a whitelist and pattern recognition on my servers.
Recently, I’ve moved to a smarter clientside solution based on Bayesian filters. A Bayesian filter is a bit of artificial intelligence that sorts and weights patterns according to logic worked out by Thomas Bayes back in the XVIII Century.
Anyway, the plug-in I’ve got is open source, cross-platform, very accurate and will grow even more so as training time increases. Perhaps you should scope this out as well.