ARC (Authenticated Received Chain)
ARC (Authenticated Received Chain), defined in RFC 8617, lets each server in an email forwarding chain add a signed record of what the message's SPF, DKIM, and DMARC results looked like before that hop forwarded it onward. A forwarded message typically fails SPF, and sometimes DKIM, by the time it reaches its final destination, because forwarding changes the connecting server's IP and can alter the message in ways that break a DKIM signature; ARC gives the receiving mail system a verifiable record that the message passed authentication earlier in its path, so it can weigh the forwarder's own reputation instead of rejecting on the final-hop failure. Both the forwarder and the final recipient's mail system need to support ARC for it to help -- support exists today among major providers including Gmail and Microsoft 365, but is not universal.
By AdminKit team, Netbase JSC · Updated