Are you aware of a superb spam filter called POPFile? I use it. It is free and it is truly excellent. For my email traffic, POPFile has so far achieved an accuracy rate of 98.23% (and still improving).
POPFile is a Bayesian spam filter. It learns as you identify email as spam or legitimate. My accuracy rate built up rapidly to 97% in a very short time. The author of POPFile, John Graham-Cummings, evidently has a deep understanding of the devious ways of spammers. Importantly, POPFile reliably identifies spam while hardly ever producing a false positive. It integrates well with the Outlooks and other well-known email clients.
I learned about POPFile in a book intriguingly titled 'Degunking your Spam, Email and Viruses' by Jeff Duntemann, publisher Paraglyph Press. I consider this the best book on general Internet security I have read and recommend it wholeheartedly to those such as me who are not 'experts'. The title hardly does this book justice.
I bring these to your attention because they are SOOOO good. I am merely the user of one and the purchaser of the other. I do not know the authors of either but consider that they deserve support and encouragement in helping to address these scourges.
Null illegitimus carborundum