Enhance DMARC By Adding the Authenticated Received Chain (ARC) Protocol
Mailgun should enhance their mail engine MTA to use the Authenticated Received Chain (ARC) protocol with all inbound and forwarded messages that go through Mailgun.
There are 2 situations where this will help. When evaluating inbound emails and the DMARC policy of the sending domain is checked and fails or when Mailgun receives an email sent to a mailing list that, in turn, sends the message to all mailing list members.
For both these scenarios, if a DMARC check is done and the original sending party has a policy of quarantine or reject, it is possible for these valid emails to either not get delivered or end up in a spam/junk folder, even though they came from a valid source but just went through multiple mail systems before reaching its final destination.
By adding ARC, the DKIM signature and SPF results are included with each hop along the way so when the message reaches it's final destination, that mail system, with ARC enabled, can look at the received chain within the mail headers and determine it came from a valid source and choose to override the DMARC policy of the originating mail system because their information is included and valid in the first hop results.
Other major ESPs like AOL and Google are already implementing this and Microsoft and Yahoo have plans to do so soon. It would be great if Mailgun also added this protocol so it could evaluate the ARC chain on incoming messages and have more successfully delivered to the recipients inbox and also include ARC information for messages sent via mailing lists or forwarded from an individual mailbox so the end receiving system has the ARC information to evaluate and determine if it is legitimate, even though it went through an intermediary mail system.
You can read more information about ARC here: