“Microsoft are now rejecting mail without a DMARC policy, but accepting mail with a policy of none. This is a massive and pointless change in their policy for incoming mail, made with no notice whatsoever.”
A DMARC policy of “none” does nothing. Microsoft now demands it anyway, and bounces valid, signed mail that doesn’t have it. They didn’t announce it, apparently didn’t mean it, and can’t figure out how to undo it. Everyone else gets to scramble with DNS changes, because when you own half the world’s inboxes your bugs become everyone’s policy.