Ever notice this?
This might not be something you want if you don’t permit users to use mobile versions of Outlook, or you aren’t prepared to support end users installing & running Outlook Mobile.
If you want to get rid of the link, there’s a registry key/value that you can set that will enable you to now remove this line from Outlook 2016’s Account Settings.
- SUPPORT: How to remove the "Get the Outlook app" link from Outlook 2016
https://support.microsoft.com/en-us/help/4010175/how-to-remove-the-get-the-outlook-app-link-from-outlook-2016
Kurt Shintaku's Blog 