It's not about configuration but rather your IP reputation and the struggle to not have your mail go straight to addressee's spam folder.
I see this reasoning as the #1 reason not to self host, but it really isn't a big issue once you do the initial setup.
Please expand on this. Public cloud IPs would be on spam lists, and providers like Hetzner and OVH aren’t any better. Where does one go to buy a decent IP?
What you will find is that many dedicated IP's from larger vendors are fine.
I personally use Hetzner and don't have any issues with reputation at all.
IME anything that can be purchased by an average developer is in some list nowadays and deliverability is always crap (with luck it lands on spam folder).