Install enigmail by entering the following commands in the terminal:
sudo apt update sudo apt install enigmail
Description:
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.
Homepage: https://www.enigmail.net/
Version: 2:1.9.9-2
Section: universe/mail