The Authenticated Received Chain, or ARC, protocol allows intermediaries in indirect mail flows, such as mailing lists, virus scanners, and forwarders, to preserve and convey authentication results they observed to the final recipient. This is inspired by the inadvertent blocking of legitimate messages routed through such intermediaries that can occur under certain DMARC policies, because forwarding causes SPF to fail and common alterations to the messages cause the sender’s DKIM signatures to no longer verify. More information about ARC can be found at the website http://arc-spec.org.