Tor and Email
Using email securely has been a challenge since shortly after its conception and continues to be to this day. By utilising Tor to create and connect to accounts, users can obfuscate their own IP and make themselves unknown to providers and hosts, as well as secure potentially deanonymising email headers. This takes a portion of trust out of the hands of third parties.
Thunderbird is a free and open-source mail client that is available for download on Windows, MacOS and Linux and is commonly found in the repositories of many major UNIX distributions. Thunderbird has built-in support for the 'Torbirdy' addon, a tool used to facilitate secure use of the email client over the Tor network.
For instructions on downloading, installing and configuring Thunderbird and Torbirdy, see this page of the documentation.