You're absolutely correct. Bayes filters made a great impact on the development of spam detection. I didn't drill down into technical details here and didn't tell about Bayesian filters as want to write a separate post devoted to them (especially to Kalman and Particle filter). Thanks for mentioning filtering of human-bots-spam. It's indeed a big challenge as an ad in messengers sometimes is utterly annoying. I think in this case messengers also use the probabilistic approach, e.g. if this contact is not from your contact list then probability that it's a spam is much higher.