Microsoft 365 Tenant to Tenant Migrations

Tenant-to-tenant migrations can be performed in the same way as other Microsoft 365 migrations, however, if the source domain name is being migrated to the destination this adds an additional layer of complexity relating to the domain name registration and CloudM Migrate licensing. This guide explains how to perform tenant to tenant migrations without running into issues. It is very important to plan ahead to minimise downtime during this process so we recommend this guide is reviewed thoroughly and all steps planned well in advance of a switchover.

If the domain is changing

If the source domain name(s) are not being migrated, then the migration can be configured and performed without any extra steps. 

If the domain is migrating

Tenant to tenant migrations that are keeping the same domain name differ because Microsoft does not allow a domain to be associated with two tenants at the same time. This means an initial migration must be performed to accounts with temporary (usual usernames, then the domain removed and added to the destination tenant and a delta migration performed.

  1. Configure CloudM Migrate to migrate from your source tenant to your destination (e.g to
  2. Migrate all historic email and OneDrive/Sharepoint data if applicable
  3. Remove the domain(s) from the source tenant
    This can be done in the Microsoft 365 admin center but all UPNs must be changed first, the following Powershell commands change all non-admin object UPNs from your source domain to a nominated other domain, and removes the domain from the source tenant (changing the domain names to the domain names referenced here).

    Admins must be changed in the admin center

    Remove legacy UPN for Tenant to Tenant Migration (using the script attached here)

    If you encounter any errors when removing the domain, ensure that all references to the domain have been removed from places such as security groups, distribution lists, users, and Office 365 groups.

    It can take as little as 5 minutes for Office 365 to remove a domain if it's not referenced in a lot of places. If there are many references that use the domain it can take up to a day for the domain to be removed by Microsoft so it is highly recommended to perform these actions at quieter times where possible, such as a Friday evening.

  4. Once fully removed, add the domain to the destination tenant and rename accounts
  5. Reconfigure CloudM Migrate to migrate from your now-renamed source accounts to the destination by changing the Export and Import Names in the userlist
  6. Perform a delta migration of all items. This should include all mail, contacts, calendar and OneDrive/Sharepoint items - If any OneDrive/Sharepoint data has been modified since the earlier bulk migration, these changes will be migrated.


CloudM Migrate licenses are assigned to each destination domain. This means that when performing the delta migration, after renaming the accounts, it will require another CloudM Migrate license. If you are running such a migration, you should contact us through your account manager or via and we will be able to provide additional licenses to mitigate this at no extra cost. See this article also.

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