Wouldn't it be nice to have a Pi-Hole mailserver.
Known spamming & malware domains being filtered out.
I think this is way way way out of scope for a DNS based adblocker.
Not DNS or something.
A mail server using kind of hosts file for filtering.
This is what puts this request out of scope, in my opinion.
Use https://sourceforge.net/projects/assp/ for that, works very very well.