Microsoft's Recent Blog Post on their new mail app make interesting reading
When we began working on the Mail app for Windows 8.1, we had a lot of customer feedback to consider. We also recognized that people use email today in many different ways than they have in the past, and that the email service you use can make all the difference. For us, that meant ensuring that the Mail app truly takes advantage of the Outlook.com service. It also led us to optimize the Mail app in Windows 8.1 for a modern mail experience—one that is efficient on mobile devices, built for touch, integrated into your whole life, and designed for the types of mail that matter most to you.