But all that complexity of migration, when similar results can be achieved today using SMTP trust-lists and separate accounts. In your roadmap example, steps 1

But all that complexity of migration, when similar results can be achieved today using SMTP trust-lists and separate accounts. In your roadmap example, steps 1 and 2 can be done right now by maintaining trusted network lists for SMTP, so that employees can't be spammed by unapproved senders. And it can enforce TLS between those trusted networks for privacy. Meanwhile the customer-service people can have both guarded @internal.bigcorp.com and open @bigcorp.com accounts, the latter for public communication. That's a pattern that's already in use and works on existing infrastructure. Any new protocol will have to offer overwhelming benefits.