Email encryption isn&#x27;t mainstream and it isn&#x27;t Thunderbird&#x27;s fault, but GPG&#x27;s. It&#x27;s an antiquated protocol with an antique implemention and it&#x27;s hard to understand and hard to setup. Thunderbird including the implementation by default would only confuse users. Those who want Enigmail already know to search for the plugin. Those who don&#x27;t know what it is wouldn&#x27;t know what to do with it.