I switched my hosting servers to Centos 7 a couple years ago, my postfix instance has been a fun experiment for the past year or so.
Below see the instance of “Blocked using” in my maillog file. The dips are when I was not using any, and the peaks are when I was using one, or many blacklist providers. I’ve heard good things about the barracuda blacklist, so I’ll add that eventually, and watch for spikes.
Important parts of my main.cf