Having managed an exchange instance for my old job, I can safely say that DKIM and DMARC are just some extra DNS entries for out-of-band verification. They can be boiled down to a pair of checkboxes on a compliance sheet.
I can also say that most of the companies we got emails from didn't have DKIM, and even fewer had DMARC. Or worse, they had DMARC set to p=ignore. Which is honestly even more infuriating.