Yeah, that's what ARC is intended to do.
Hum. My understanding of ARC is that it's a way for a server to assert things about what it received. - Where as my interpretation of what we were discussing is the sender authorizing intermediary MTAs to send the message. The former is after the fact, and the latter is before hand.
I did a draft of a double signing thing that let the sender say who's expected to sign a modified forwarded version. The big mail systems weren't interested. They want the recipient system to decide. https://datatracker.ietf.org/doc/draft-levine-dkim-conditional/ Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly