I’m bummed that TorBirdy is no longer being actively maintained, but I hope everyone uses Thunderbird, sets the proxy settings to go over Tor with the Tor Browser Bundle, and uses Riseup’s onion addresses for the mail servers. I do this all while connecting over the Riseupvpn too (love that it’s so easy to install). Hopefully someone publishes a script at some point that settings the timezone to UTC, converts eveyrthing to plain-text, etc and makes the client much safer (which TorBirdy used to do), but at the very least I think connecting over a secure network and using GPG is strong, given the surveillance state is the most common threat we face.