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OnPrem Exchange Server

Dahabiyeh, Bahlal 0 Reputation points
2025-08-08T12:16:48.1866667+00:00

Inherited a new environment and trying to make sense of things.

We are Exchange Online; there are no hybrid setup settings in either online or the on prem exchange server.

But we do use Azure AD for AD sync.

New users, shared mailboxes, etc do not show up in the recipients on the onPrem Server.

The only thing that is the shame for both Exchange online admin center in the onPrem is the Organization sharing. Not sure if this is even needed?

So not sure what this exchange server is actually doing?

I manage all aspects of recipient information from Exchange online.

Thanks

Exchange | Exchange Server | Management
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  1. Hin-V 2,000 Reputation points Microsoft External Staff Moderator
    2025-08-08T14:33:14.74+00:00

    Hi @Dahabiyeh, Bahlal

    Thank you for inquiry and welcome to Microsoft Q&A.

    Allow me to clarify your concern, the on-premises Exchange server in your setup (with Azure AD Connect for directory synchronization but no hybrid configuration) serves a specific, limited purpose: it provides the necessary schema extensions to Active Directory and management tools (like the Exchange Admin Center or PowerShell) for handling Exchange-related attributes of user accounts in your on-premises AD. These attributes, such as proxyAddresses (email aliases), legacyExchangeDN, showInAddressBook (for GAL visibility), and others, these attributes then synchronized to Azure AD and Exchange Online via Azure AD Connect.

    For more detail, you can refer via: Exchange Server hybrid deployments

    You also concern If this is needed?

    The answer is yes, as long as Azure AD Connect is syncing your on-premises AD to the cloud, Microsoft recommends keeping at least one on-premises Exchange server (or equivalent management tools) for proper attribute management and support. Decommissioning it entirely would break the ability to manage synced users' Exchange attributes without workarounds, which aren't officially supported. If you're not actively using the on-premises EAC for changes, it might be idle but still essential for the schema/sync foundation.

    Additionally, you mention "Organization Sharing Settings". The similarity you're seeing here is probably coincidental or a remnant of initial setup. In a non-hybrid environment, these settings (e.g., for external calendar sharing or federation) aren't actively integrated between on-premises and online. They might appear similar if manually configured the same way, but the on-premises server isn't facilitating any cross-organization sharing with Exchange Online. If you're not using features like federated sharing, this overlap isn't providing value and could be ignored or reviewed for cleanup.

    If you have any additional concern, feel free to comment below. I be more than happy to assist.

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".      

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