From RC3.org:

I’ve found that the more a software product costs, the less likely it is to work properly, and the harder it will be to implement.

Which is why you should use Free Software. I won’t say it is easy to implement, or always works properly, but I will say that procmail or spamassassin works better than TrendMicro’s $5000 eManager Content Plug-in (which we use at work)