Back in the day ('noughties through 2015 or so) there was POPFile, which did Bayesian classification of emails for spam filtering. John Graham-Cumming wrote it,

Back in the day ('noughties through 2015 or so) there was POPFile, which did Bayesian classification of emails for spam filtering. John Graham-Cumming wrote it, and it worked reasonably well. I still think of him as the POPFile guy first, then remember he's the Cloudflare CTO. A more advanced classifier certainly do better these days.