Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
GrexIt - Manage Tasks, Customer Support and Sales right from your Gmail inbox. Turn your Gmail into a powerful collaboration tool.
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Mailor - Shared inbox, team portal and smart notifications
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Airmail for iOS - One of the best Mac email clients, now on iPhone