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Last thing to do is to give the Azure app the permission to send emails via the Microsoft Graph API.
To do perform this, from the app's overview page, go to API Permissions > Add a Permission > Microsoft Graph > Application Permissions. Use the search bar to search for "Mail", Select Mail list and tick "Mail.Send" and you can tick "User.Read" if you want to see the list of users who can use this Azure app. Add the permissions to grant your Azure app the permission to send emails.
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