How To Perform An Office 365 Tenant-To-Tenant

Migration With The Same Domain

Tenant-to-tenant migrations within Microsoft 365 (previously known as Office 365) are becoming more prevalent due to factors such as mergers, acquisitions, and organizational restructuring. These migrations tend to be relatively simple when there is no overlap in domains; however, migrating with the same domain adds a layer of complexity. This complexity arises from the fact that a domain can only be associated with one tenant at any given time.

In this article, we will outline the steps and considerations necessary for executing a successful tenant-to-tenant migration in Office 365 while using the same domain. Get additional details here.


Understanding the Challenges of Same-Domain Tenant Migrations


Why Same-Domain Migrations Are Unique

In Microsoft 365, you can only have a single instance of a custom domain (like yourcompany.com) active in a specific tenant at any moment. Consequently, to connect the domain to the desired tenant, it needs to be eliminated from the original tenant first. This elimination process requires disconnecting the domain from all users, groups, and services in the original tenant, which can be quite challenging in a busy business setting.


Planning is Key

As your domain will need to be offline for a short period during the transition, it is crucial to plan and schedule meticulously. Typically, organizations choose to carry out these migrations on weekends or during low-traffic times to reduce both downtime and interruptions.



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Step-by-Step Guide to Office 365 Tenant-to-Tenant Migration with the Same Domain


Step 1: Prepare Both Source and Target Tenants

Begin by collecting essential information regarding both the source and destination tenants:

  • Licensing information

  • User count

  • Domain settings

  • Mailbox capacities

  • Current workloads (Exchange, SharePoint, Teams, OneDrive, etc.)

Verify that the destination tenant possesses adequate licenses and resources to accommodate the incoming data and users.


Step 2: Create User Accounts and Assign Licenses in Target Tenant

It's advisable to set up user accounts in the destination tenant in advance. This can be accomplished either by hand or by using PowerShell scripts. Make sure to allocate the required licenses (such as Exchange, SharePoint, Teams, etc.) to these accounts to guarantee that services are ready before the data migration.


Step 3: Prepare the Source Tenant for Domain Removal

In this phase, you need to disassociate the domain from every user, email address, proxy address, group, Teams channel, and resource within the source tenant.

  • Update the primary SMTP address for users to a temporary domain (for instance, user@tempdomain.onmicrosoft.com).

  • Eliminate any domain mentions in mail flow rules and connectors.

  • Disconnect the domain from Exchange Online, Azure AD, and various Microsoft services.

After ensuring no remaining active references, it is safe to delete the domain from the source tenant.


Step 4: Add and Verify the Domain in the Target Tenant

Once the domain is detached from the source tenant, it can be incorporated into the target tenant:

  • Access the Microsoft 365 Admin Center in the target tenant.

  • Introduce the custom domain and confirm ownership through DNS verification.

  • Configure the necessary DNS records (MX, SPF, DKIM, etc.) to direct email traffic to the new tenant.

Keep in mind that DNS updates may take a while to take effect, so be sure to account for this in your planning.



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Migrating Microsoft 365 Workloads


Exchange Online (Mailboxes)

Consider utilizing a migration solution from a third-party provider, such as BitTitan, Quest, or Cloudiway, for mailbox transfers. These tools facilitate staged and cutover migrations, enable coexistence, and help minimize downtime.


SharePoint Online & OneDrive for Business

Utilize either Microsoft's SharePoint Migration Tool or alternative third-party options to transfer site collections, documents, permissions, and metadata. It's important to ensure that URL mappings are accurately preserved during the process.


Microsoft Teams

Migrating Teams can be intricate and often necessitates the use of external tools to facilitate the transfer of channels, files, chat logs, Planner tasks, and tabs. It's important to ensure that users are accurately aligned with their Teams in the destination tenant.


Testing and Post-Migration Tasks


Perform Validation Checks

Once the migration is complete, ensure the following:

  • Email communication is functioning properly.

  • The DNS settings are accurate and have been fully propagated.

  • Mailboxes and their contents remain undamaged.

  • Access to SharePoint and OneDrive files is available.

  • Team features are fully operational for every user.


Decommission the Source Tenant (Optional)

After the new tenant is fully set up and users have moved over, you may proceed with decommissioning the original tenant, if necessary. Be sure to back up any remaining data before this step.