rules better than bayes?

[jo3]

Hi,

This is an observation, please take it in the spirit in which it is 
intended, it is not meant to be flame bait.

After using spamassassin for six solid months, it seems to me that the 
bayes process (sa-learn [--spam | --ham]) has only very limited success 
in learning about new spam.  Regardless of how many spams and hams are 
submitted, the effectiveness never goes above the default level which, 
in our case here, is somewhere around 2 out of 3 spams correctly 
identified.  By the same token, after adding the "third party" rule, 
airmax.cf, the effectiveness went up to 99 out of 100 spams correctly 
identified.

So far, we have not had a single ham misidentified as spam with over one 
million messages examined.

Throughout the documentation, there seems to be a bias toward the bayes 
filter rather than the rule system.  Does anyone on the list have some 
thoughts which would help to explain my observation as to why a single 
rule would appear so successful while a million spams and hams would 
have so little effect?

Thank you,
Jo3