BeaverMail
Open-source mail, private by default.
BeaverMail comes in two products. Use either one on its own, or both together.
BeaverMail desktop app
Mail, contacts and calendar in one app for Windows, macOS and Linux. Works with Gmail, Microsoft and any other mail provider, and never sends your data to us.
BeaverMail Server Early release
Run your own mail server for your domains, with security, spam filtering and a web console built in. For Debian and Ubuntu.