I do agree that trusting the domain instead of the exact user is more than enough in the case of the article. What I'm saying is that PGP has the whole trusting thing built-in. Key distribution can be done through DNS (there is an OPENPGPKEY record: https://tools.ietf.org/html/rfc7929) or through HTTP (https://tools.ietf.org/id/draft-koch-openpgp-webkey-service-...).

On the other hand there is nothing existing today for telling your MTA to trust this or that domain only. There is no standard so every provider would start by doing their own thing. That missing part is the difficult part, and that is only doable in pgp today.

However it is true that in both cases there should be some UI indication to ask you "do you trust this domain ?"