The link uploads the add-in in the Exchange admin center.
Optional, enabled by default: Enable the add-in by default and allow your users to turn off the add-in.
Optional, disabled by default: Disable the add-in by default and allow your users to turn on the add-in.
Mandatory, always enabled. Users can't disable this add-in: Enable the add-in by default and do not allow your users to turn off the add-in.
According to Microsoft, it can take up to 72 hours for a newly deployed add-in to appear on the app ribbon in your users' Outlook mailboxes. Your users may need to relaunch Office to view the add-in icon on the app ribbon.