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How to Execute a Tenant-to-Tenant Microsoft 365 Migration

When Office 365 first came out, organizations were skeptical about their tenants existing in a shared service. These concerns made many companies shy away from fully-adopting cloud technology. But over time, these companies came to trust and accept that the controls kept in place could keep tenants separate.

Unfortunately, these same controls posed migration challenges in mergers, acquisitions, or divestitures when organizations’ need to combine tenants arose. Consequently, migration options are now very limiting. Microsoft does provide a few basic cross-tenant migration options, but these are still in Public Preview.

As the number of Microsoft 365 and Office 365 adoptions among organizations increases rapidly, so does the need for migrating and consolidating tenants. To further complicate the matter, some companies have multiple accounts. Consolidation within one organization reduces costs and operational complexities.

Currently, there is no straightforward method that could walk you through the entire Microsoft 365 tenant-to-tenant migration process. Therefore, if you want to migrate email between tenants, you need a third-party migration tool.

This article looks at the process of cross-tenant migration in Microsoft or Office 365 and its primary challenges.

Executing a Microsoft 365 Tenant-to-Tenant Migration

Let’s look at the process of migrating mailboxes and service settings between two Microsoft 365 organizations. Organizations with over 500 users or a significant amount of SharePoint data should consider a Microsoft Solution Provider when migrating.

1. Planning

Microsoft 365 migration is a massive undertaking with many technical processes and a lasting impact on the organization. Therefore, it’s essential to plan your migration at least two weeks beforehand to avoid unforeseen disruptions. Planning includes taking measures to ensure you meet all pre-requisites for the migration and have acquired all the necessary licenses for third-party migration tools.

2. Preparing Tenants

Next, prepare the target tenant to receive the migrated mailboxes. Ensure that it can accommodate new mailboxes. Create objects like Rooms, Groups, Users, and Resources from the source tenant in the target tenant – either manually from the Microsoft 365 admin center or through Azure Active Directory consolidation.

3. Informing Stakeholders

Inform everyone affected by the migration. The communication should include details of the migration such as expected time of completion, steps they should take after the process, advisory to notify all end-users about the change of services, and whom to approach for assistance.

4. Preparing the Domain and User Accounts

During the migration, you will have to merge the source Microsoft 365 tenant with the target tenant. To do this, add the source tenant to the target’s Microsoft 365 admin center and create TXT records for DNS verification. Your IT team should also generate a CSV file of all the email addresses scheduled for migration to the target mailbox because of third-party migration tools. It’s prudent to append “.onmicrosoft.com” to all source tenants’ email addresses.

5. Updating Mail Exchanger (MX) Records

Change the server address receiving emails on behalf of users to match the target tenant. Changing the MX records address will disrupt email flow, so you need to keep this period, referred to as time to live (TTL), to the least possible value.

Find a third-party service to queue your emails for a period (days or weeks) and deliver them to the new Microsoft 365 organization once complete.

6. Disabling Azure Active Directory Syncing

The Azure Active Directory allows access to public folders, applications like SharePoint Online, and other related resources. Force it to stop syncing before migrating accounts, a process that could take almost one day. Schedule this step on a non-working day.

7. Source Tenant Preparation

You have to remove the source tenant domain from Microsoft 365 to complete the migration. To do this, you will need to reset email addresses, SharePoint Online public websites, and other relevant objects back to the original domain. Additionally, remove secondary licenses and revoke the affected ones before migrating accounts. Use Windows PowerShell command to stop all processes blocking the removal.

8. Target Tenant Preparation

Next, verify the transfer of accounts and domain in the target domain’s admin center. Additionally, configure the Azure Directory for the new domain and assign licenses to users for mailbox activation. Furthermore, assign the old email addresses as the primary addresses. They will begin receiving emails after the completion of the MX record updates.

9. Moving Objects to the New Accounts

To complete the migration, you need to move all objects to the new accounts, including contacts and calendars. Use the appropriate migration method (staged, cutover, or hybrid migration) depending on the Exchange Server and Microsoft 365 tenants.

10. Migration Day Activities

When you plan your migration well, you will have few activities on the migration day. These include stopping the source tenant from receiving emails, configuring the source tenant’s domain move to the target tenant, verifying the domains, and proceeding with the best migration method selected.

11. Post-Migration Cleanup Steps

You need to clear the Outlook Auto-Complete List (the nickname cache) to solve any issues that arise, such as migrated emails’ replies not getting delivered successfully.

Microsoft 365 Cross-Tenant Migration Challenges for Common Workloads

The Microsoft 365 tenant-to-tenant migration is not without its share of challenges, which include the following:

  • Exchange Online: Substantial volumes of Microsoft Exchange characterize tenant-to-tenant migrations because many users fail to clean up their mailboxes. As a result, this creates migration challenges such as reducing the speed and function of the process.
  • OneDrive for Business: For tenant-to-tenant migration of Microsoft 365, the most significant impact is the actual sharing of data and not the data move. Another challenge is large data volumes.
  • Microsoft Teams: These can present a significant obstacle since Microsoft has not provided APIs to enable Microsoft Teams’ data migration. For now, you can recreate the teams and channels and re-add members, but it’s a slow process, particularly if you have many remote workers.
  • SharePoint Online: Custom Applications and bespoke customizations present a migration challenge, especially if you have to do many mini-migration projects to accommodate the numerous other applications running alongside SharePoint.
  • Yammer: Currently, no APIs support Yammer migration.
  • Flow, Power Apps, and Stream: These are still not migration options, and users have to recreate what they had.

Over to You

Microsoft 365 tenant-to-tenant migration is often a result of mergers, acquisitions, or divestitures. You require proper planning and a competent IT team to handle the migration efficiently and deal with the unique challenges that the process poses.

In The Cloud Technologies specializes in Microsoft 365, Microsoft Teams, and Microsoft Azure Services. We help clients in Boston, MA, and the larger New England region maximize their Microsoft cloud services and solutions. We can help you conduct a seamless Microsoft 365 tenant-to-tenant migration. Reach out to our team for help or expert assistance.