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
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Express Mail - Best mobile email app for Salespeople
myMail - myMail is the smart email app for managing all your accounts on iOS and Android.
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.