Optional: Add more email protection with Tor
The Onion Router (Tor) network wraps Internet communication in multiple layers of encryption and bounces it around the world several times. When used properly, Tor confuses surveillance field agents and the global surveillance apparatus alike. Using it simultaneously with GnuPG's encryption will give you the best results.
To have your email program send and receive email over Tor, install the Torbirdy plugin the same way you installed Enigmail, by searching for it through Add-ons.
Before beginning to check your email over Tor, make sure you understand the security tradeoffs involved. This infographic from our friends at the Electronic Frontier Foundation demonstrates how Tor keeps you secure.