Changing Exchange Forest Hosting Exchange Hybrid


  • Hi 

    We have a single Exchange Forest - Legacy. The Exchange namespace for Legacy is Company A.

    Legacy presently hosts Exchange server infrastructure (mbx servers etc) and Exchange Hybrid infrastructure. All mailboxes have been migrated from Legacy into Exchange Online.

    We are using AAD Connect (to sync identities into O365) and ADFS. Both of these are hosted in Legacy

    We desire to have another AD Forest (Future) host an Exchange Organisation and to host the Exchange Hybrid infrastructure. The Legacy and Future AD forests whave a trust relationship configured between them. We must preserve the Company A namespace in Future.

    No mailboxes will be hosted in Future - as i understand it we need only preserve an Exchange server in Future for AAD Connect and ADFS (for Management).  Nor is there any requirement to establish connectivity between the Legacy and Future Exchange environments.

    Given that we must have unique namespaces for each Exchange Forest what is the best approach to deploying Future? Are we able to change the namespace in Legacy ( to say Company B) deploy Exchange in Future with Company A namespace? What would the implications be for the Hybrid Configuration etc?

    Please let me know if i not explained this correctly and i will try to clarify.


    • Edited by grimey73 Wednesday, July 4, 2018 10:49 AM
    Wednesday, July 4, 2018 10:33 AM

All replies

  • Hi,

    Yes, we must use unique namespace for each Exchange forest if you want to deploy hybrid environment with Office 365.

    In current situation, we recommend to configure a new namespace in new AD forest. And, it's supported to configure multiple AD forests with single Office 365. Figure as below:
    After hybrid deployment with multiple forests

    Moreover, if you want to migrate account and mailbox to new forest, we can use ADMT and Prepare-MoveRequest.Ps1 to migrate from original forest to new forest, and deploy hybrid with new forest.

    Best Regards,
    Allen Wang

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Thursday, July 5, 2018 6:55 AM
  • Hi,

    It has been a long time since you made the last post on this thread. If you could get any help from the above posts, please be free to mark them as answers,  it will be easy for other community members to find the useful one/ones.

    Thanks for your understandings!


    Manu Meng

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact

    Click here to learn more. Visit the dedicated forum to shareexplore and talk to experts about Microsoft Teams.

    Monday, July 23, 2018 5:46 AM