Last week I upgraded to Mailman 2.1.18 in order to get the DMARC workarounds new in that version. I set dmarc_moderation_action for my list to "Munge From" and waited to see what would happen. Despite that I seem to still be having DMARC bounces, as this morning I got 22 "Bounce action notifications" for list subscribers from Mailman.
I'm running the just-released RPM for 2.1.18 on Fedora 20. I have the python-dns package installed, which I read was required for DMARC checks. When I grep my logs for 'DMARC', all I see are the bounce messages in my Postfix log---so if the DMARC checks that should be made when a post from a yahoo.com account comes to the list are failing, they're failing in a way which isn't showing up.
There is one unusual thing about my list---namely that it sits at one end of a bridge to a phpbb forum. That is, all of the posts from the forum are posted to the list with their Sender set to a special address which is subscribed to the list, and all post from the list are received by that special address and posted to the forum from there. This means that a lot of the addresses in From headers of messages going out over the list are not actually subscribers to the list. Could this be tripping up the dmarc_moderation_action?
-- J.