We want to go cloud only with Exchange online, but documentation suggests that we must have an Exchange server on-premises since we have EntraID connect for directory synchronization. Is this true?

Question

We have Microsoft Exchange online in a hybrid configuration with one single Exchange 2016 server. I noticed that Exchange 2016 and 2019 are EOL in October 14 of this year, which means that we may need to migrate to Exchange Server SE on premises to keep hybrid continuity. 

Microsoft documentation suggests that we keep the hybrid configuration alive and retain at least one Exchange SE server online due to the fact that we have Azure AD connect in place for identity synchronization.

My question is this: is there a way to retain directory synchronization through Azure AD connect, while being in an Exchange Online only state? I'm looking for some guidance from seasoned Exchange/Exchange Online admins who can advise us on this. 

Answer 1

Hello, @@Jamie McFarling,

Welcome to the Microsoft Q&A platform!

Traditionally, maintaining an on-premises Exchange server is recommended for hybrid configurations, especially with Azure AD Connect for directory synchronization. However, you can fully migrate to Exchange Online while retaining Azure AD Connect for directory synchronization. You can consider options like Azure AD Connect Cloud Sync, a lightweight agent that synchronizes your on-premises Active Directory with Azure AD but doesn't support writeback to on-premises.

(Relevant issue: Azure AD Connect cloud sync and Exchange Online only? - Microsoft Q&A)

Third-party tools can manage Exchange attributes without an on-premises server, or you could manually manage these attributes using tools like ADSI Edit or PowerShell scripts.

Once your mailboxes are fully migrated, you can decommission the last Exchange server by converting on-premises mailboxes to mail-enabled users in Active Directory. This process will lose some GUI management tools, but you can manage necessary attributes using PowerShell or third-party tools.

Should you need more help on this, you can feel free to post back. 

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Best Wishes,

Alex Zhang

Answer 2

Hi @Jamie McFarling

If you still sync your user from on-prem to Entra ID using Entra Connect server, synced objects can be modified only from active directory.This is the reason why Microsoft recommend to keep at least one Exchange server even though all mailboxes are migrated to Exchange online in order to be able to edit Exchange attributes using Exchange server.

Here a thread talking about the same subjects:

Best Practices for Decommissioning On-Prem Exchange Server After Migration to Exchange Online

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