The best Windows email client is a matter of personal preference, as different clients cater to various needs and preferences. eM Client offers customization and integration with video chat and cloud storage, while Thunderbird provides a free and open-source option with a vast add-ons library. Microsoft Outlook provides a robust business platform with advanced features, but its interface may not appeal to everyone. Mailspring is a simple and easy-to-use client that's great for those who miss Windows Mail, while Mailbird offers numerous integrations and a modern interface. Twobird turns your inbox into a to-do list, and WunderMail brings Gmail to the desktop as a native app with offline support. Ultimately, the best email app is one that works for you, so it's recommended to download a few and try them out before making a decision.