Earlier quoted context omitted.
This is somewhat true. RFC3207[1] describes opportunistic TLS encryption for SMTP communications. Our postfix deployment uses this and a fair amount of our email is sent over TLS-encrypted SMTP. Of course, an MITM attack could hide the STARTTLS option and there are questions around the strength of the CA cert infrastructure, but SMTP is not just plaintext. [1] https://tools.ietf.org/html/rfc3207
The problem is that all of the people you correspond with use gmail, which participates in PRISM. No amount of transport encryption or storage encryption on your own end will stop Google from sharing that data with US authorities.
The whole protocol and mail delivery system is fucking hopeless.
As an ex-ISP mail architect and ex-operations guy, I hope the whole existing email protocol suite and architecture dies in a fire.