This can be caused by webview being disabled. This registry key can be set in the following location:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\Webview
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Webview
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Office\15.0\Outlook\Webview
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\15.0\Outlook\Webview

The registry entry in any of the locations above is called Disable and has a value of 1.

The example above is for Outlook 2013. If a different version of Outlook is installed the registry location will change from 15.0 to the relevant value:-

14.0 - Outlook 2010
16.0 - Outlook 2016

Check the locations mentioned above for the existence of the registry entry. Change the value from 1 to 0.

Warning: Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.

When opened within Outlook EVS appears as a blank page.