> You get a clean error message that tells you exactly what to do

We are literally talking about a situation where this is not happening! And the problem is that it's not just this. Once you give them a license to police e-mail, they start policing e-mail for all kinds of arbitrary and inscrutable reasons. If this were going to be done, it should really be formalized as an industry standard by an independent consortium, not up to the whims of Microsoogle.

Are we? Microsoft is bouncing emails with instructions on what to do.

DMARC, DKIM and the rest are industry standards set through an independent consortium (it's called the MAAWG iirc)