enigmail | Enigmail - GPG support for Thunderbird | Mehr ...
OpenPGP extension for Thunderbird. Enigmail allows users to access the features provided by the popular GnuPG software from within Thunderbird. . Enigmail is capable of signing, authenticating, encrypting and decrypting email. Additionally, it supports both the inline PGP format, as well as the PGP/MIME format as described in RFC 3156.