Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Roundcube - Web-based IMAP email client
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Shift - Shift is the ultimate email client for managing Mail, Calendar, Drive, Slack, Asana, Jira, Evernote, and all your other favourite apps
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.
Polymail - Native email app for email productivity.