Clearing a Bayes SQL user
(pasted from a mail:)
You shouldn't check mail for non-existent users.
The best way to clear this data is via sa-learn.
sa-learn -u <nonexistent user> --clear
You can get a list of usernames from the bayes_vars table, it is not the id column it is the username column.
If you don't really have the ability to not check mail for non-existent users you might want to check out this plugin: http://wiki.apache.org/spamassassin/AuthzUserPlugin