Nothing sketchy about self hosting your email. Sure, that is what the big tech cartel wants you to think so you're forced to let them handle your correspondence "for your own safety". Don't believe their lies.
Issue isn’t self hosting email, it’s self hosting it at .xyz.
They had one of the cheapest registration costs. And so ended up with a high concentration of spammers compared to older established tld’s like dot com. Using the tld for legitimate purposes is really challenging due to the high number of systems that flat out blacklist it.
Making assumptions on someone's right to communicate based on their choice of email domain is discrimination, and only serves to drive people to their walled gardens.
I'm not the one making assumptions, it's thousands of independent hosts, and all big tech orgs (including specifically Apple in this case) who are making that assumption. I didn't say the assumption was right, just that it's trivial to avoid falling afoul of it by choosing to use a different TLD.