https://www.ritlabs.com/en/products/thebat/
The Bat! - Secure Desktop Email Client for Windows 10
The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.
secure desktop emailbatclient
https://tuta.com/blog/desktop-clients-tutanota
Free secure desktop email client for Linux, Windows and macOS | Tuta
Why the Tutanota desktop client is best for productivity and security.
secure desktop emailfreelinux