TL;DR Email - Send short emails & read emails as fast as you read Facebook
Polymail - Native email app for email productivity.
mlist - Email newsletters, outside of the inbox
Revo Mortgage Collaboration - Revo is a cloud based deal management service, it addresses the missing technology gap for mortgage application process and workflow management for high volume mortgage producers and their assistants using a cloud based CRM service solution
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
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.