I belong to a couple Yahoo groups.Here is their policy on DMARC
 
DMARC-related changes in Yahoo GroupsFollowing the recent changes in Yahoo DMARC policy to protect users from email spam, we’ve made changes to how Yahoo Groups sends mails to members’ inboxes.When a member of a Yahoo Group replies to a post, mails are sent by Yahoo Groups on behalf of the user. The message is sent with the “From” email address as <groupname>@yahoogroups.com, and the display name in “From” would contain the email address of the sender and the name of the Yahoo Group.
Message sent by Yahoo Groups on behalf of the user used to appear as:
From: “My Name” <[log in to unmask]>
With the change, it would be:
From: “ ‘My Name’ [log in to unmask] [groupname]” <[log in to unmask]>
When replying to a Group message, Group “Reply-To” settings of the Group will continue to be honored on the Reply compose screen on the web and in your email service.
On the web experience, if you choose a “To” address other than reply to the group, like ‘reply to sender’ or ‘reply to group owner’ (using the drop-down menu), the “Reply to” mail address would be changed appropriately.
For example, if you choose to ‘reply to the sender,’ replies to your email will be delivered to your actual email address, even though the “From” address of your reply will have:
“ ‘My Name’ [log in to unmask] [groupname]” <[log in to unmask]>
With these changes we are addressing deliverability issues due to DMARC adoption by mail service providers.
- Yahoo Groups team
 
> Date: Sat, 10 May 2014 19:35:29 -0700
> From: [log in to unmask]
> Subject: [ARSCLIST] Yahoo mysteries, etc.
> To: [log in to unmask]
>
> Cross posting in case you haven't seen this:
>
> <http://www.dmarc.org/>
>
> explains a lot, not necessarily all good!
>
> <L>
> Lou Judson
> Intuitive Audio
> 415-883-2689