When you attempt to install Dynamics 365 App for Outlook, the Status column shows "Issue when adding to Outlook". When you click the "Learn more" link, you see a dialog with the following details:
There was an issue when attempting to add the app to Outlook.
Crm : IncomingEmailS2SApprovalNeeded
There was an issue when attempting to add the app to Outlook.
Crm : IncomingEmailS2SApprovalNeeded