Enigmail extension for Thunderbird
Enigmail - GPG support for Thunderbird and Debian Icedove
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.