You may need to connect Microsoft Office Online for example when connecting to the Outlook Add-in for Office 365. To do this please navigate to your my profile page in the top right-hand corner. You will need to click into your my profile in order to access the settings.
Once in your my profile please navigate to: Microsoft Outlook Online. From there you will want to click on "Connect".
You will then need to connect to your Microsoft account to successfully connect Microsoft Outlook Online