Dear Maintainer,
While I agree that the feature has been marked as EXPERIMENTAL, it's been in Exim4 for years now. Sender requirements are enforced by GMail ever more strict and ARC signing is one of them. I too run into the problem that exim4 in Debian doesn't have this feature enabled.
Switching to postfix and rspamd would be an option, if it didn't depend on redis, which is unnecessarily complex for our setup.
Thank you for considering the request. Regards, Erik.
