Enigmail is a Thundberbird plugin which will allow you to encrypt your emails using OpenPGP.
As we previously wrote on our blog, you should consider sending encrypted emails whenever you're writing about personal things that you only want to reveal to your receiver.
Encryption can be a pain but luckily Enigmail makes this easy for anybody using Thunderbird.
Encrypting and decrypting messages only takes a click and you can verify the signatures of messages received.
Enigmail uses OpenPGP, which is a very good, open source encrypting solution. Since it works as a Thunderbird plugin, it's also small and unintrusive and integrates perfectly in the Mozilla mail client.
Enigmail brings some advanced configuration, which could still turn off some users. For one, you'll need to install GnuPG by yourself to make it work.
However, take the time to delve into the preferences and you'll have encryption well set up in Thunderbird. You'll be able to choose your key, select to sign encrypted and non-encrypted messages by default or not and if to send an OpenPGP header with your messages.
Enigmail is flexible encryption tool, which lets you edit rules by recipient, manage smartcards and handle all your keys via one interface.
In all, if you use Thunderbird, this plugin is definitely a must, so that you can send encrypted emails.
Although some users will be afraid of the configuration, Enigmail is a very efficient and flexible encryption plugin for Thunderbird.