I posted on my blog about this issue in April here: http://blog.jasonsherry.net/2014/04/10/dmarc-broke-your-mailing-lists/
I had hoped to find some work around by now, but still haven't.
The issue occurs if you host a DL (Distribution List\Groups) that contains external recipients and external recipients can send to this DL. In my case I host 20+ DLs+ for friends and family that contain many external recipients. basically running a ListSrv using Exchange.
The issue, starting in April when Yahoo.com and now Aol.com, is that the DMARC policy on some mailsystems is set to Reject. So when a yahoo.com user sends an e-mail to DL@company.com and this DL then sends the message to members at aol.com, yahoo.com, msn.com, comcast.net, hotmail.com, and others it will be rejected. The reason is that these e-mail providers check the DMARC policy for the domain the message shows up as coming from. In this case the message was sent from user@yahoo.com, but got forwarded by Exchange to the DL members. The From address will show user@yahoo.com, but the actual sending server was Exchange, not Yahoo. So the e-mail is rejected, causing a NDR talking about the DMARC policy in many cases.
One option is to setup a Mailbox and put the DL e-mail address on it and then have a Rule set on the mailbox to forward mail to the DL. But I really don't want to create 20+ mailboxes and set this up.
So has anyone, with Exchange, figured a better solution?
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Microsoft Infrastructure Architect, MCSE: M, MCTIP, Microsoft Exchange MVP