K-9 for Android is one of the best email clients available on any platform today. This open source application implements support for many different protocols and comes with a host of useful features.
“OpenKeychain helps you communicate more privately and securely. It uses high-quality modern encryption to ensure that your messages can be read only by the people you send them to, others can send you messages that only you can read, and these messages can be digitally signed so the people getting them are sure who sent them.”
“In a world of repressive governments and a growing reliance on insecure networks, there’s no way anyone can be sure their most sensitive messages aren’t intercepted by the forces of darkness. But you can make it mathematically improbable that all but the most well-funded snoops could ever make heads or tales of your communications.” Use Dan Goodin’s step-by-step guide to email encryption and keep your communications private.
“You too can get PGP set up in a few simple steps.” Jason Thomas shows just how easy it is to start encrypting your messages.