It really is "that bad". I've been running mailservers for decades now. It really is.
It is impossible to use a VPS from any sizable or affordable VPS servers. The IP blocks from digital-ocean, linode, AWS, OVH, etc all are, have been, or will be randomly put on blacklists. Not the blacklists that you can apply for to be deregistered from. It's sheer impossible to have mail from a mailserver on any such host delivered to hotmail, gmail or such.
It is impossible to run a server at home. "domestic" IP addresses are treated similar to those of affordable VPS providers.
It is expensive to get a clean and proper IP address. It takes years of serious volume to give an address any authority. It takes only one mistake by any of the thousand typists at hotmail or gmail to undo this investment. Without any way to recover from it. None of these large mailproviders have any incentive to improve this: an "engineer" at their end making a "mistake" actually benefits them.
I've ran a mailinabox for as long as the project exists. But I'm sunsetting it moved everything to tutanota (but don't like the service so will move to an alternative in january). I just gave up: the monopolies have won.