Interesting what AI has to say... what do you say?
Since you are a veteran self-hoster (25+ years), I can give you the "technical reality" answer rather than the marketing one: The days of successfully self-hosting email for critical delivery are effectively over.
The major providers (Gmail, Outlook/Microsoft, Yahoo/AOL) have formed an oligopoly. They trust each other's IP ranges implicitly, and they treat almost everyone else (VPS providers like DigitalOcean, Linode, or residential IPs) as "guilty until proven innocent."