The latest version of the Bananatag Add-in for Outlook 365 users is available from the Microsoft Store. This version of Bananatag will be available for OWA users as well as Outlook for Mac 2016. To install it using the desktop version of Outlook for Mac 2016...
Access the Store from the main ribbon of Outlook for Mac 2016, and search for "Bananatag":
Click on the Bananatag Add-in listing to view more details about the add-in, and enable it by selecting Add. The add-in can also be immediately enabled by clicking Add on the previous page.
The Bananatag Outlook 365 Add-in will how be accessible inside Outlook for Mac 2016.
Note: If the Store link is not visible in the main ribbon of Outlook, or if the Bananatag Add-in does not display on the main ribbon after being added, it's likely that the inbox currently being accessed is not a 365-enabled address. The Microsoft Store, and any enabled Add-ins, will only display when a 365-enabled inbox is selected in Outlook.