You Can’t Escape Gmail
Do you avoid Gmail due to privacy concerns? Your resistance is futile. Benjamin Mako Hill has hosted his own email for the past 15 years, and despite that, he found that over half of his email messages either come from or go to a Gmail account, where they can be analyzed by the search giant’s automated algorithms. Of course, the same is roughly true of other large mail hosting firms, so although the mail you send isn’t likely to allow these companies to target ads at you better, it’s far from being a private communication between you and the recipient.
In addition, the thing that many people still don't realize is that SMTP (Simple Mail Transfer Protocol) is inherently not a secure protocol. SMTP is not only the protocol that's used to send outgoing mail from your mail client, it also transfers mail between all of the various servers on the 'net as it makes its way from your ISP to the recipient's ISP. Even if you use SMTPS on your computer, that only encrypts the mail as it is sent from your computer up to your ISP. It's still unencrypted as it moves across the rest of the 'net. That means that not only can the receiving ISP (like Gmail) store and analyze the contents of your messages, any of the network providers in between also can do exactly the same thing.
So, really, the smart thing to do is to think about email as a postcard, where the mailman or any of the mail sorting clerks can easily read it, not a sealed letter. Sending the email equivalent of a sealed letter requires that both the sender and recipient use encryption.
Not accurate. STARTTLS has existed for years to secure IMAP, POP3, and SMTP.
http://en.wikipedia.org/wiki/STARTTLS
Facebook just last week posted about how they use it and how many servers they send mail to accept it. It's a lot of them. And more than half even support Perfect Forward Secrecy.
https://facebook.com/notes/protect-the-graph/the-current-state-of-smtp-starttls-deployment/1453015901605223