Update April 12, 2014: Yahoo has confirmed the DMARC change in an official statement. There appear to be no plans to revert this change. If you're using yahoo.com in your from address, it's advised that you use an alternate 'from' email domain. For now, a private domain or other free email provider will work, though a private domain is preferable since other free email providers may follow Yahoo's lead.
Update April 22, 2014: AOL has announced changes to their DMARC policy as well, so you'll want to use alternatives for AOL addresses in the 'from' field as well.
Late last week, Yahoo! quietly made a dramatic change to the DMARC policy for yahoo.com that impacts senders who use services like Mandrill or independent mailing lists to send 'from' @yahoo.com addresses. Yahoo hasn't indicated exactly why they made this change, but it may signal other changes from email providers that are yet to come.
If you're sending through a service like Mandrill, you can generally use your own email address as the 'from' email address. For site and app owners, this is usually an address on their domain. For some use cases, though, the 'from' address might be a personal email address like a Gmail or Yahoo address. Email's generally designed to allow this - you can send 'from' an email address through any server on the internet.read more