They're just bouncing mails for the hell of it now. I've had all my DNS ducks in a row for years, nobody bounces mail on me except now Outlook has started. And when I send an email that goes to a human for review, that person has written back saying it all looks in order, but can't do anything about it.
I think they've just gone to whitelisting providers that are big enough that the stink they'd raise would be more trouble than what I can make for them.
Fuck Microsoft.