Decommission Exchange Server in Cross-Forest AD migration (mailboxes in Exchange Online)

Ashutosh Kumar 20 Reputation points
2024-10-07T23:12:58.8833333+00:00

I am currently working in an environment where we are migrating from Forest A to Forest B. The purpose of this migration is to transition to a new domain, and using the rendom tool is not an option.

Current Environment:

  • Mailboxes: Previously hosted on on-premises Exchange, but they have now been migrated to Exchange Online. We still have the on-premises Exchange server in place for mail flow.
  • Hybrid Configuration: The Hybrid Configuration Wizard (HCW) has been enabled, and we have Hybrid Azure AD Connect configured with hybrid enabled settings in the source environment.
  • Email Applications: Some applications are currently using the on-premises Exchange server to send emails.

Migration Plan:

  1. AD Migration: We have finalized the timelines for the Active Directory migration and plan to use Active Directory Migration Tool (ADMT).
  2. Azure AD Connect: After migrating all objects to the destination forest, we plan to disable AD synchronization in the source environment. Instead of importing the Azure AD Connect settings from the source, we are considering re-creating the configuration for the Azure AD Connect tool in the new forest, using mS-DS-ConsistencyGuid as the source anchor.
  3. Mail Flow: Once we have established mail flow with the Exchange mailboxes authenticating against the new forest's Active Directory, we intend to decommission the source environment's Exchange server.

Request for Advice:

I would like to receive suggestions on how to effectively plan this migration to avoid any disruption in mail flow during the transition. Specifically, I am concerned about:

  • Ensuring continuous mail flow while migrating objects to the new forest.
  • Configuring Azure AD Connect in the new environment without causing synchronization issues.
  • Any additional considerations or best practices to follow during this migration process.

Thank you for your assistance!

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Accepted answer
  1. Alex Zhang-MSFT 1,600 Reputation points Microsoft Vendor
    2024-10-08T08:35:38.93+00:00

    Hello, @Ashutosh Kumar,

    Welcome to the Microsoft Q&A platform!

    Based on your description, I understand that you have a comprehensive plan for migrating from Forest A to Forest B and would like some advice on how to ensure a smooth migration.

    Migrating Active Directory (AD) and ensuring uninterrupted mail flow can be a complex process, here are some tips to help you make a smooth transition.

    About how to ensure continuous mail flow while migrating objects to the new forest, the following steps are recommended:

    1.Properly configure the Hybrid Configuration Wizard (HCW) in both forests, which will help maintain mail flow during migration.

    2.Ensure that the mail flow between Exchange Online and the local Exchange server is configured correctly by sending and receiving test emails.

    If you want to configuring Azure AD Connect in the new environment without causing synchronization issues, here are some things to keep in mind:

    1.When setting up Azure AD Connect in a new forest, use mS-DS-ConsistencyGuid as the source anchor point, which will help maintain consistency and avoid synchronization issues.

    2.Use Azure AD Connect in staging mode in the new forest, which allows you to verify configuration and synchronization without affecting the production environment. Once all objects are migrated to the new forest, disable AD synchronization in the source environment to prevent any conflicts.

    As for additional considerations and practices to follow during this migration process, please refer to the following points:

    1.Before the formal migration, set up a test environment to simulate the migration process, identify possible problems, and verify the effectiveness of the solution.

    2.Ensure that you have up-to-date backups of all data prior to migration and have an emergency recovery plan in place to prevent data loss due to unexpected issues.

    3.Implement a mail flow monitoring tool during the migration process to monitor the transmission of emails in real time and identify and resolve transmission failures in a timely manner.

    4.Regularly review Exchange and Azure AD Connect logs to identify potential errors or warnings that can provide important troubleshooting information.

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

    Thank you for your support and understanding.

    Best Wishes,

    Alex Zhang

    1 person found this answer helpful.

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