To use the OpenPGP features in Thunderbird, you need to set up a so-called personal key pair for your email address. You can do this in the End-to-End Encryption subsection of your account settings. If you already use OpenPGP with other software, you will need to import a backup copy of your existing key. Otherwise, you can create a new key.
≡ > Account Settings > Select your account > End-to-end encryption > Add key...
If you already have a personal OpenPGP key pair from other software, select Import existing PGP key .
If you don't have a key yet, select Create a new OpenPGP key .
After importing or creating, still in the account settings, select the key you want to actively use in your email account.
Please note that using OpenPGP has consequences as described in the general introduction. It is very important to back up your keys and store them in a secure location separate from your regular computer.
I have used Enigmail before, how do I migrate and configure it?
You can upgrade your Thunderbird settings from older versions (e.g. 68.x) to version 78.x. It is recommended homeowner database that you back up your old Thunderbird profile before using Thunderbird 78 for the first time, because once you upgrade, your profile will no longer work with Thunderbird 68. A backup will allow you to easily go back if you decide for any reason that you must continue using Thunderbird 68 and Enigmail.
Enigmail currently has two versions, 2.1.x and 2.2.x:
Enigmail 2.1.x only works with Thunderbird 68 and earlier, and provides classic features.
Enigmail 2.2.x versions are specially modified versions that only work with Thunderbird 78 and higher. Enigmail 2.2.x does not provide legacy features, but instead helps you migrate your keys and settings to Thunderbird 78.
If you start Thunderbird 78 with an existing profile, and the previous profile had Enigmail installed, Thunderbird 78 will detect that the previous Enigmail 2.1.x add-on is incompatible. It should automatically check for a newer version, it will find Enigmail 2.2.x and install it. Enigmail will then automatically open a tab, greet you and say that migration is possible, and offer to start it.
Enigmail uses GnuPG to store and manage all keys and trust settings. If you click the button to start the migration, the Enigmail migration software will read your old keys from GnuPG one by one. You must enter your password to confirm the export of your keys from GnuPG and allow them to be unlocked to import them into Thunderbird's new internal key storage.