If you upgraded to Windows 8.1 and tried to access Outlook Web App with the new Internet Explorer 11, you probably noticed that the “Use the light version of Outlook Web App” checkbox is checked and disabled on the login page:
That means that IE11 is willing to render only the basic version of OWA which was originally designed to target legacy browsers. This is quite embarassing, because IE11 is a really modern browser even in the preview! The solution is to force IE to render OWA in compatibility mode. You can add the site to the compatibility list in the Tools –> Compatibility View Settings dialog: Click Add button
IF the above settings didn’t resolve the issue then try to add your OWA URL to the list of sites in the Intranet Zone in the Tools –> Internet Options –> Security –> Local intranet –> Sites –> Advanced dialog.
According to some forum posts, the same issue arises with Office 365 and some popular websites like GitHub as well.