In your letter dated Tue, 20 Dec 2016 17:35:44 -0500 you wrote: >On Tue, Dec 20, 2016 at 07:56:01PM -0000, John Levine wrote: >> Whether a mail system enforces DMARC policies is up to the system's >> manager, not individual users. Even in the IETF, I expect that many, >> perhaps a majority, of users have only the dimmest idea what if >> anything their operator does with DMARC. > >This starts getting more complicated, but the mailing list could try >intentionally sending a message which fails DMARC (e.g., with a >claimed from address of example@xxxxxxxxx) to the mailing list >subscriber and see if it gets bounced, and use that to set the default >for that setting automatically? Typically, a user whose mail system rejects too many e-mails is automatically unsubscribed. There are a range of possibilities, from just adjusting the boiler plate in the unsubscribe notice to automatically turning the option on when a reject involves a DMARC protected sender. As for Randy's suggestion. That would be equivalent to turning the option on for everybody. That may also be a sensible default. People who want to reply directly can turn the option off manually. Just always rewriting DMARC protected From headers is suboptimal for recipients that don't want to have anything to do with DMARC. Why subject them to broken From headers?