Mail-in-a-box [0] has a very good mail filter. Junk mail is about at Gmail levels for me, with almost zero false positives and almost zero false negatives. Some of my accounts are fairly high volume and I have found its performance to be very acceptable.

The fact that I can host as many domains and accounts as I want with all kinds of filters and rules and forward them all to my main account as needed with rules is just gravy.

[0] https://mailinabox.email/