Microsoft Dynamics 365 Business Central requires an Azure App Registration to integrate with other Microsoft products like Outlook and SharePoint. This also applies for Apportunix apps like Document Archive and Document Mail Queue.
The Azure App Registration facilitates the authentication and authorization between Business Central and the Microsoft identity platform. When you create an Azure App Registration you establish a trust relationship between the Microsoft products and Business Central. In the registration you can control the supported account types, redirect settings, certificates & secrets and the permissions.
In this short how to video Megan Weidema will show the process step by step: