Yet more special pleading. This argument might make sense if it was claimed that Google, Yahoo etc were doing this for some corporate agenda. But I am pretty certain that is not the case here. Google, Yahoo etc. are doing this because they think it is in the interests of their customers because they believe it will reduce spam. A legitimate argument against DMARC would be 'Here is a research study based on empirical evidence that shows DMARC does not help'', it might not be persuasive but it would be a valid argument to have. I am certain that the Google, Yahoo, Microsoft, etc. folk have those studies. So what is the argument being made against? I see a lot of hypotheticals and I see a lot of people arguing that the real problem here is that Google, Yahoo and Microsoft are putting what they consider to be the best interests of their customers ahead of compliance with purported IETF diktats. I find the arguments that IETF should ignore the impact of DMARC unpersuasive. We have changed email repeatedly in response to non standards compliant actions taken by the spam senders. So there is a precedent for responding to malicious actions, why would we treat non-malicious actions differently? We are engineers, not priests. If people think DMARC is creating a problem then explain the problem precisely and find a solution.