DMARC & Mailing Lists: A Roundup

In 2014, Yahoo and AOL both implemented strict "p=reject" DMARC policies on their primary domains. This presented challenges to both AOL/Yahoo users and various service providers. Yahoo implemented this new DMARC policy in February. AOL implemented the sample policy in April.

In particular, this makes delivering mail more challenging for discussion mailing list providers. A number of them have had to implement header changes to "play nice" with DMARC restrictions.

• Google Groups implemented DMARC-compatible header changes in April, 2014.
• Yahoo Groups implemented DMARC-compatible header changes in May, 2014.

Running your own mailing list manager? Here are my suggestions on message checks and header changes that you should consider implementing into your discussion list software. They approximately mirror what Google and Yahoo have implemented. (And some savvy commercial groupware/list management software publishers were quick to implement similar changes.)

Some mailing list managers have decided to reject signups from users at AOL and Yahoo. I recommend against taking this stance; your list of rejection domains is only going to grow as additional ISPs and domain owners implement DMARC policies similar to what AOL and Yahoo have done.

Yahoo is not likely to roll this back any time soon. They find their new DMARC policy choice to have been a success. AOL likely feels the same way.

Additional Frequently Asked Questions:
Ask Al: Is my personal domain affected by DMARC?
Ask Al: Should I add a DMARC record to fix the Yahoo issue?

If you run the mailing list manager software Mailman, here you'll find information on how to configure Mailman to work within the confines of DMARC restrictions.

Keep in mind, if you implement any DMARC-related DNS changes for your domain, be sure to test! If you do DMARC wrong, you're setting yourself up to have your mail rejected.