DMARC is estimated to cover at least 60% of the world's mailboxes.
That's an interesting number, but how was it computed/counted,
and what does it mean in reality.
It certainly means Gmail, Yahoo, Hotmail, AOL, and all their various
hosted services such as AT&T ISP mail in the US, as well as giant US
cable ISP Comcast.
When the @yahoo.com reject policy had been set up, I checked whether
I could send fake @yahoo.com Email to my private German (F)reeMail
account and to my own company email account, and both Emails were
properly delivered to my Mailboxes.
It's more popular among large providers than small ones.
R's,
John