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
Morning Mail - A new way to manage your mail. Tinder for email.
Newton Mail - Newton is a fully featured mail client available for Android, iOS, macOS and Windows.
Polymail - Native email app for email productivity.
Aqua Mail - Android Mail Client.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.