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 Outlook Web App (OWA) users as well as Outlook for Mac 2016. To install it using your Office 365 OWA mailbox...
Open the Settings menu by clicking the gear icon on the main ribbon of Outlook 365's webmail interface at https://outlook.office365.com/owa, and navigate to Manage add-ins:
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 OWA as well as the rest of Office 365.
Note: If the Store link is not visible in the settings menu, or if the Bananatag Add-in does not display on the creation of a new email 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.