Mail-Addin not working properly in the Outlook desktop application

Some parts of the add-in doesn't work in the desktop application but works when you use the addin in Google Chrome. You might be able to see parts of the UI but can't save a todo.

Any add-in that runs in the desktop version of Microsoft Outlook actually runs in Internet Explorer.

Things to verify:

Ensure that you have the latest version of Internet Explorer 11 installed.

Sometimes Outlook.exe is configured to run in emulation mode and therefore uses an older version of Internet Explorer than the version installed.

You can check that by opening the Windows registry and browse to

HKEY_LOCAL_MACHINE (or HKEY_CURRENT_USER)
   SOFTWARE
      Microsoft
         Internet Explorer
            Main
               FeatureControl
                  FEATURE_BROWSER_EMULATION
                     outlook.exe = (DWORD) version

If the outlook.exe doesn't exist it means that it's not running in emulation mode, which is good.

If the key has a value it means that it runs in emulation mode. Solve this by:

1. taking a backup of the FEATURE_BROWSER_EMULATION folder and then
2. removing the outlook.exe key.

If you experience problems afterwards, restore the registry key with the backup.