> How come self hosting email is such a pain in the ass?
Because Google and Microsoft have a monopoly on email.
Because of that, they don't have to play nice with anybody else and can make you jump through any arbitrary number of hoops since they hold most of the users.
It's very uneven, and which domain(s) you have trouble with will not necessarily be the same as anyone else's problem domains. I also self-host, no mailing lists, personal mail only, and my one and only deliverability problem is AT&T. Google? OK. Comcast? OK. Charter? OK. Hotmail? OK. Any @sbcglobal.net address, or anything else associated with SBC d/b/a AT&T? Fahgeddaboudit. I can check the public DNSBLs, and there's no problem. I can jump through AT&T's hoops, and get their automated replies, and next week I try to send to a person on AT&T and find I'm back on their secret blacklist.
Because Google and Microsoft have a monopoly on email.
Because of that, they don't have to play nice with anybody else and can make you jump through any arbitrary number of hoops since they hold most of the users.