DKIM Access Control and Differential Changes

This document specifies a DKIM (RFC 6376) extension that allows cryptographic verification of SMTP (RFC 5321) envelope data, of any DKIM signature along the message path, even beyond IMF (RFC 5322) message content changes. It therefore addresses security glitches, and introduces a new world of email solutions that move complexity away from lower network layers, where problems cannot be solved, complying with David Wheeler's fundamental theorem of software engineering, that "We can solve any problem by introducing an extra level of indirection". It updates DKIM to obsolete certain aspects that reality has proven to be superfluous, incomplete, or obsoleted.