About DMARC on lists.debian.org
DMARC (https://wordtothewise.com/2014/04/brief-dmarc-primer/) is a great thing.
To protect our subscribers we (Debian listmasters) will probably have to reject mails from every domain that enforces rejects via DMARC (p=reject) in the future. If you want to follow the discussion subscribe to Bug #752084. That means that users of such providers will not be able anymore to post to our lists without using a third party service.
I can only encourage users of such providers ( aol , yahoo I mean you!) to tell their providers how shitty DMARC is. By the way, rumors say that this will include all gmail users in the future.
If you want to laugh, there are some solutions for handling DMARC: