Yes, spam classification is a solved problem. Perhaps even at the level of "this is new IP address with no reputation, is it sending 80% spam or 80% ham?" kind

Yes, spam classification is a solved problem. Perhaps even at the level of "this is new IP address with no reputation, is it sending 80% spam or 80% ham?" kind of questions with some defined precision at scale, but ceratinly at personal mailbox level, if you own and train your own clasification engine with thousands of samples of ham and spam you actually receive. That's very effective, and much better than my past experience with gmail.