disable/prevent HMA data sync to cloud

Question

hello,

we are a regulated Organization that we cannot sync and users data to cloud.
however we are implementing Intune with HMA "hybrid Modern Authentication" for users in-order to monitor and control devices, the issue is that the data sync is preventing us from completing the setup.
as per the article :
https://learn.microsoft.com/en-us/exchange/clients/outlook-for-ios-and-android/use-hybrid-modern-auth?view=exchserver-2019

(""The Exchange ActiveSync (EAS) connection between Exchange Online and the on-premises environment enables synchronization of the users' on-premises data and includes four weeks of email, all calendar data, all contact data, and out-of-office status in your Exchange Online tenant. This data will be removed automatically from Exchange Online after 30 days when the account is deleted in Azure Active Directory."")

my ask, is there a way to disable the sync between the exchange online and the on-premise environment.

Answer 1

Like Andy mentioned above, your requirement is not able to achieve.

The link also list the Technical and licensing requirements

Active Directory Synchronization. Active Directory synchronization of the entire on-premises mail recipient directory with Azure Active Directory, via Azure AD Connect. Outlook for iOS and Android uses the tenant's Exchange Online Global Address List for on-premises mailboxes that leverage hybrid Modern Authentication. If all mail recipients are not synchronized into Azure Active Directory, users will experience mail flow issues.

Answer 2

No, you can't use the Outlook Mobile app if that is a requirement.

The disclaimer further below in the document you linked above spells that out for Government tenants ( and really any that do not allow syncing to the cloud)

On-premises accounts leveraging hybrid Modern Authentication with Outlook mobile are not supported with Office 365 US Government Community and Defense tenants, Office 365 Germany tenants, and Office 365 China operated by 21Vianet tenants.

Answer 3

Did anything come about this question? I would like to take this question further, in that the article/link in the original question also states, "Data synchronization between the on-premises environment and Exchange Online happens independent of user behavior".

Does this mean once Hybrid Modern Authentication is enabled mailbox data begin to sync to EXO? How can an Admin confirm and check the location where these mailboxes reside in EXO? It's not the same as user mailboxes, as we currently have no users in EXO however we have HMA enabled.