[caf]

The use of TLS (which is what uses a CA-issued certificate) isn't to prevent phishing attacks, it's to prevent emails being read or modified in transit.

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 "[e-mail]" though, and I don't know that there really is a good technical solution to that sort of thing.

[lucaspiller]

> to prevent emails being read or modified in transit

Except everything you send and receive with your Gmail account is read by them and whatever government agencies anyway... So what's the point?