The volume of e-mail cloaked in encryption technology is rapidly rising as Google, Yahoo, Facebook and other major internet companies try to shield their users' online communications from government spies and other snoops.
Google and other companies are now automatically encrypting all e-mail, but that doesn't ensure confidentiality unless the recipients' e-mail provider also adopts the technology.
In an analysis released on Tuesday Google said that about 65 per cent of the messages sent by its Gmail users were encrypted while delivered, meaning the recipient's e-mail provider also supports the technology.
That's up from 39 per cent in December. Incoming communiques to Gmail were less secure. Only 50 per cent of them were encrypted while in transit, up from 27 per cent in December.
Encryption reduces the chances that e-mail can be read by interlopers. The technology transforms the text into coding that looks like gibberish until it arrives at its destination.
Google and other internet services rely on a form of encryption known as Transport Layer Security, or TLS. Security experts say that encryption method isn't as secure as other options.
But encryption that is tougher to crack is also more complicated to use.
Gmail, with more than 425 million accounts worldwide, was one of the first free e-mail services to embrace TLS.
Yahoo, Facebook and AOL are also encrypting their e-mail services. Microsoft, whose stable of e-mail services includes the Outlook, MSN and Hotmail domains, has started encrypting many accounts as part of a transition that won't be completed until later this year.
Less than half of the correspondence from Hotmail accounts to Gmail wasn't encrypted as of late May, Google said.