TL;DR Email - Send short emails & read emails as fast as you read Facebook
Mailbutler - Mailbutler adds lacking functionality to email clients and increases your productivity
mlist - Email newsletters, outside of the inbox
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.
Dispatch - Email parsing for sales leads