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

Question

We have completed the migration of all our mailboxes to Exchange Online.

Currently, we are syncing users from Active Directory to Entra ID through the Entraconnect server.

What are the best practices for decommissioning our on-premises Exchange environment?

Answer 1

Hi @LULU-6701

You can proceed to cleanup your Exchange servers but If you still sync active directory user , you should keep at lease one Exchange server on-prem in order to be able to modify On-PREM Exchange attribute synced from active directory to Entra ID because synced objects can be modified only from on-prem envirement..

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Answer 2

Hello LULU-6701,

Thanks for your question.

On-premises Exchange might still be managing key attributes synced to Entra ID. You need to verfiy if this is the case in exchange. Also backup any remaining data on the Exchange server, such as logs, message tracking, or configuration settings.

If all of the users will be managed in Microsoft 365 or Office 365, and there are no other directory synchronization requirements, you can safely disable directory synchronization and remove Exchange from the on-premises environment. See detailed steps for decommisioning here: https://learn.microsoft.com/en-us/exchange/decommission-on-premises-exchange#to-disable-directory-synchronization-and-uninstall-exchange-hybrid

You can mark it 'Accept Answer' and 'Upvote' if this helped you

Regards,

Abiola

Answer 3

Assuming you meet the pre requisites, you can remove that last Exchange Server and manage from on-prem via powershell:

https://learn.microsoft.com/en-us/exchange/manage-hybrid-exchange-recipients-with-management-tools

Otherwise:

https://learn.microsoft.com/en-us/exchange/decommission-on-premises-exchange#why-you-may-not-want-to-decommission-exchange-servers-from-on-premises

Answer 4

Hello, @LULU-6701,

Welcome to the Microsoft Q&A platform!

The Microsoft experts above have provided comprehensive and effective advice on best practices for deactivating local Exchange environments, and I would like to share an issue with similar requirement s and its resolution to you.

Issue link: Removing On-Premises Exchange Servers after Migrating to Office 365 - Microsoft Q&A.

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

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If the answer is helpful, please click on ACCEPT ANSWER as it could help other members of the Microsoft Q&A community who have similar questions and are looking for solutions.

Thank you for your support and understanding.

Best Wishes,

Alex Zhang

Answer 5

As you said, you’ve migrated all the mailboxes to EXO. Microsoft recommends keeping one Exchange server if you are syncing users from Active Directory to Entra ID to manage email attributes. Also check the email flow, it should be completely managed by EXO. Also before decommissioning, take backup of everything. The process for this has been mentioned by MVPs above.