The TorBirdy extension configures Thunderbird (or Icedove, etc) to make connections over the Tor anonymity network. It also takes steps to protect anonymity at the application level by reducing unique identifiers, disabling unsafe plugins, disabling insecure protocols, helpfully configuring other software such as Enigmail and GnuPG in anonymity protecting ways and more. It also helps to ease configuration with other anonymity networks and proxies such as JonDos.