Experts from the Internet Engineering Council, specialized in email infrastructure and spam filtering claimed this in the Yahoo breaks every mailing list in the world including the IETF’s.” on Internet Engineering Task Force (IETF) John R. Levine claims Yahoo! has established a new rule to automatically exclude Yahoo users from the mailing list, because Mailing List server does not comply with DMARC requirements and they strongly modifies each email. This weakness in the mailing lists is not just restricted to Yahoo! subscribers, in fact the subscribers at Gmail, Hotmail, Comcast etc are also facing it.
Source: https://thehackernews.com/2014/04/yahoos-new-dmarc-policy-destroys-every.html