Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Roundcube - Web-based IMAP email client
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
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.
Rainloop - RainLoop is a web based email client.