in my experience, if there is a Bayesian filter score and you combine it with other scores, the composite score will be less reliable. i had SpamAssassin on an email server that i ran for years and i wondered why spam kept leaking through and when i disabled everything but the Bayesian filter, it started working better. on a later email server i just dropped SA in favour of Bogofilter - the original Bayesian spam filter which does nothing else - and it did the same job. a Naive Bayesian Classifier library should be able to do the same job. and NIP-05 verification is just a token you add as an input to the classifier. it'll learn to recognise that token as a good sign if you train it enough.