Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Newton Mail - Newton is a fully featured mail client available for Android, iOS, macOS and Windows.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Aqua Mail - Android Mail Client.