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

LULU-6701 341 Reputation points
2025-01-14T22:09:50.5833333+00:00

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?

Windows for business | Windows Client for IT Pros | Directory services | Active Directory
Exchange | Exchange Server | Management
Exchange | Hybrid management
Microsoft Security | Microsoft Entra | Microsoft Entra ID
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  1. Thameur-BOURBITA 36,261 Reputation points Moderator
    2025-01-14T22:19:35.4833333+00:00

    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..


    Please don't forget to accept helpful answer


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  1. Abiola Akinbade 29,490 Reputation points Volunteer Moderator
    2025-01-14T22:24:19.2266667+00:00

    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

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  2. Andy David - MVP 157.8K Reputation points MVP Volunteer Moderator
    2025-01-14T23:30:23.25+00:00
    1 person found this answer helpful.
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  3. Anonymous
    2025-01-15T03:00:06.78+00:00

    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. 


    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

    1 person found this answer helpful.

  4. Amit Singh 5,306 Reputation points
    2025-01-15T04:41:30.38+00:00

    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.

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