Fastmail clearly reached out to Apple eons ago, which is evidence of skill on fastmail's part and not favortism on Apple's part. Admittedly, fastmail very likely has lots of contacts in Apple (Jeremy Howard isn't nobody), but that's also a skill issue.
It’s also very interesting that Apple reached out to the user in the developer forum thread after they raised it as an EU DMA issue.
You cannot send Push notifications to the stock iOS Mail app no matter how hard you try. They can. There are functions inside of iOS that are made better because of this (auto copied 2FA codes, for example).
I'll just take your word for it that there's no ways for Texans to get the same treatment as these other companies. Oh well. Take it up with your legislature, I guess.
It sucks that Apple won't just embrace interop with host mail services in some formal way, I'm not sure what the benefit of this specific flavor of gatekeeping achieves. It also sucks that HN contrarians are reflexively dumping on this, instead of supporting entrepreneurs like one might hope in such a community. Anyway, keep up the great work, I'm with you long term.