Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Missive - Team communication app now supporting FB, Twitter & SMS
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Mailtrim - Email lives forever!. Reinvigorate your emailing experience with the best free email client, the Mailtrim