Apple has deployed a system called Private Access Tokens that allows web servers to verify if a device is legitimate before granting access. This works by having the browser request a signed token from Apple proving the device is approved. While this currently has limited impact due to Safari’s market share, there are concerns that attestation systems restrict competition, user control, and innovation by only approving certain devices and software. Attestation could lead to approved providers tightening rules over time, blocking modified operating systems and browsers. While proponents argue for holdbacks to limit blocking, business pressures may make that infeasible and Google’s existing attestation does not do holdbacks. Fundamentally, attestation is seen as anti-competitive by potentially blocking competition between browsers and operating systems on the web.
This hasn’t been practical for a while now. If you’re not on a major domain, Google, MS, etc will block you as likely spam.
Cannot confirm, somewhat. Setting it up so you don’t get blocked is rather easy, figuring out how to do that correctly is a bit of a pain though (I only managed to correctly set things up once I started using Mailcow and their built in DNS check tool)
The domain still lands on some blacklists but that is down to one ISP blanket banning any mail servers in the IP block my ISP rotates my IP through.