Usually when a major web browser decides to do something that has the potential to break existing websites they do extensive testing and put the call out for dev feedback before they release. Why didn't that happen here? Also it's odd that Chrome decided to explicitly whitelist some sites. Surely that's an admission that their automated workflow doesn't actually work well?
Google is starting to show a pattern of addressing the concerns of the large players (which themselves are a part of), and ignoring or degrading everyone else's experience. Good luck trying to get predicable deliverability to gmail without your mail being put in the spam box as a small mail sender. Google refuses to even tell you anything about why or why not mail is being delivered unless you send hundreds of messag…
Try fastmail, it's really great.