Earlier quoted context omitted.
Now I can just get a free cert and turn on TLS. What's the problem, exactly? Most people are not capable of running their own mail server. The convenience of services like Google, plus the risk of turning your mail box into a spam machine, vastly outweighs the downsides for most people.
My first concern is, if nowadays is so easy to get your certs signed by a CA how can "Authenticated/Encrypted" emails successfully prevent phishing attacks? In my modest opinion there are many week points in X.509 and how CAs are verifying identities, and even if this things were fixed you still have the problem of state-sponsored attacks that have no solution within the current www pki. I personally have no problem…
DKIM (which does not use a CA-issued certificate, it uses a public key published in DNS) is the technology that's intended to authenticate the email sender. It still wouldn't stop phishing attacks where the purported email sender is something like "admin@facebook-account-verification-2016.net" though, and I don't know that there really is a good technical solution to that sort of thing.