As reported on the Mailop list today, Yahoo has modified their Yahoo Groups discussion group service to "play nice" with posts from subscribers at domains behind a restrictive DMARC policy. Google recently implemented very similar changes to its Google Groups service. Both are believed to have done so in response to Yahoo and AOL having recently both implemented strict "p=reject" DMARC policies, affecting Yahoo users' and AOL users' ability to participate in some mailing list discussion forums.
Yahoo is modifying the original from address header to make the sending email address the Yahoo Group address and moving the original from address header to an X-Original-From header.
Yahoo Groups, Google Groups, mailman, and others services and software packages have been updating their handling of from addresses recently, in response to the challenges posed by restrictive DMARC policies that prevent off-network, unauthenticated uses of certain domain names in a from address. I've updated my own mailing list manager software similarly, and I'm sure you'll be seeing more of the same from other mailing list services and software packages in the near future.
Operators of discussion mailing lists and similar services pretty much have two possible choices for how to respond to this type of issue: Modify their software to write the from address to cooperate with this policy change, or lock Yahoo and AOL users out of participating in these various services and discussion groups; this course of action that doesn't seem widely accepted or adopted. Most list managers want their subscribers to be able to continue to participate, and most commercial service providers seem to not want to deny participation to a large swath of internet users. And certainly, one concern I've hear is, what happens when the next large ISP or webmail provider implements a similar policy?
May 15, 2014 update: Yahoo explains their changes to Yahoo Groups here.
(May 13, 2014 author note: I had an unfinished, half-written blog post in my draft queue trying to answer the question "What of Yahoo Groups?" I was basically going to say that it wouldn't surprise me to see Yahoo Groups update their service similar to how Google has done. Guess there's now no need to finish that one up.)