Hiri

Hiri is a beautiful desktop email client that helps you get your email under control and focus on the emails that really matter to you. Hiri is particularly suitable for people like managers who receive a lot of email and want to improve their communication skills.
Notable features include:

Works with Exchange, Office 365 and Outlook.com;
Includes a fully functioning calendar;
Works with your company’s address book;
Tasks and email are side by side;
Set email reminders so you don’t forget about them;
Convert an email to a task by dragging it to the Task list - simple!
Stop checking mail too often. This is a bad habit that destroys your focus. Hiri has a dashboard timer that reminds you not to check too often.