Experimental ARC
wikipedia.org:
Authenticated Received Chain (ARC) is an email authentication system designed to allow an intermediate mail server like a mailing list or forwarding service to sign an email’s original authentication results. This allows a receiving service to validate an email when the email’s SPF and DKIM records are rendered invalid by an intermediate server’s processing.
ARC is defined in RFC 8617, published in July 2019, as “Experimental”.