I use a Firefox and Thunderbird Add-on called Crypto Data CryptoData – Get this Extension for 🦊 Firefox (en-US) to encrypt some of my messages.

Programs like this have some draw backs in regard to their “unbreakability”, but do not require any key distribution. To use effectively, one must select a unique key and get that key to the recipient of the message to use in decrypting the message. My friends and I meet over a cup of coffee to exchange keys. Ken