I can't get Bayes running with postfix!
After following instructions like those at http://advosys.ca/papers/postfix-filtering.html on installing SpamAssassin with postfix, you may find that Bayesian filtering does not function as expected even after installing DB_File and rebuilding the database with sa-learn --rebuild. spamassassin -D --lint indicates no problems.
In those instructions, SpamAssassin is run via a script triggered by a "filter" line in master.cf. The filter is run by a new user, postfilter, rather than as your own user. Changes made to your Bayesian databases are not seen by this user.
You can still setup Bayesian filters systemwide. To do this, see SiteWideBayesSetup .