Geary - Geary is an email application built for GNOME 3.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
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Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Sylpheed - Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.