Thunderbird has slowed down its development but still has a dedicated pool of users. If you're still running its excellent email client but are concerned about privacy, the anonymous browsing client Tor has released a tool to protect your email called TorBirdy.
The add-on automatically connects to the Tor proxy when you log in to your email, ensuring that your location isn't disclosed. It's a simple add-on, but if you don't want your email linking back to your location, it's a good step to take. The add-on is still in beta, but it's available now if you'd like to try it for yourself.