Outlook App(Android & IOS) Can't connect internally (Exchange 2016)

[Anjello Mari Sabaricos]

Build: Exchange 2016

Exchange Configuration: Internal only (OWA, ECP, ActiveSync, Outlook Anywhere, EWS)

External only is SMTP (send/receive email)

Already downloaded the updated Outlook app,  Internally, using the android Outlook app. for setting up the Exchange, it returns "Unable to login: The Service is curretly offline. Please try againlater. If the proble persists, please contact customer service. (701)."

This same behaviour happens with IOS Outlook App. As per exchange support, Outlook app. doesnt allow pure internall exchange, would like to confirm if its true? and if not, is there possible ways to troubleshoot this concern and make it possible? is there a specific ports or address that we need to allow or to whitelist?

Thank you. 

[#2]

Afaik for on-premises Exchange, the Outlook app still uses the server-based cache, which is currently still using AWS. There are plans to move it to O365 (the Outlook app for ExO already switched to using the "native" mailbox data), but that will still depend on you having external connectivity. Anyway, @Tony Redmond should know more.

[#3]

Just want to know if we can use Outlook mobile apps internally? and there's other way around to use it only in internal connection.

Thanks.

[#4]

In either case (using the old AWS framework or the new one based on Azure - https://www.petri.com/outlook-ios-android-dumping-aws-q3), the Outlook clients need to be able to contact the service that hosts the cache of mailbox data used by the clients for features like the Focused Inbox. As both AWS and Azure are external to your network, the clients need that connectivity.

I have not seen an announcement from Microsoft to say that on-premises Exchange now uses Azure. It might be the case that this will come at Ignite.