Why is continuous configuration of anti-spam filters necessary within an organization?

Question

anonymous · Answer

Because the companies sending out the spam are also continuously adjusting their messages to get around the spam-filter rules that are in place

anonymous · Answer

I thought bayesian spam filters update themselves :(

anonymous · Answer

Even bayesian spam filters have their disadvantages ( http://en.wikipedia.org/wiki/Bayesian_spam_filtering#Disadvantages ) and so I'm sure more effective techniques will be discovered, and then more effective ways around them. The cycle continues...