Re: Thought Outlook Mobile was cloudy and uses Azure even for on-premises Exchange accounts
No AC, you remember where MS first bought Acompli, it used an AWS instance to talk to the Exchange server and the app talked to the AWS instance. Then MS changed the backend to Azure but apart from that the architecture remained unchanged, it was still a cloud backend talking to the Exchange server and the app talking to the cloud backend.
And here is a diagram from MS themselves.
As it's unnecessary I would have thought approval would not have been forthcoming, but it seems they don't care that much.