Polymail - Native email app for email productivity.
Really Good Emails - A large collection of good product email design.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
Email Love - Email design inspiration, templates and discovery
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
Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.