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Office 365 Tenant To Tenant Data Migrations 

There are several architecture approaches for mergers, acquisitions, divestitures, and other scenarios that might lead you to migrate an existing Microsoft 365 tenant to a new tenant. Most customers work with Microsoft Consulting Services or a Microsoft partner to migrate tenants, including using third-party tools to migrate content.

Office 365 Tenant to Tenant data migrations 

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Commonly, during mergers or divestitures, you need the ability to move your users' Exchange Online mailboxes into a new tenant. Cross-tenant mailbox migration allows tenant administrators to use well-known interfaces like Exchange Online PowerShell and MRS to transition users to their new organization.

Users migrating must be present in the target tenant Exchange Online system as MailUsers, marked with specific attributes to enable the cross-tenant moves. The system will fail moves for users that aren't properly set up in the target tenant.

When the moves are complete, the source user mailbox is converted to a MailUser and the targetAddress (shown as ExternalEmailAddress in Exchange) is stamped with the routing address to the destination tenant. This process leaves the legacy MailUser in the source tenant and allows for coexistence and mail routing. When business processes allow, the source tenant may remove the source MailUser or convert them to a mail contact.

Do not use this feature to migrate mailboxes on any type of hold. Migrating source mailboxes for users on hold is not supported.When a mailbox is migrated cross-tenant with this feature, only user visible content in the mailbox (email, contacts, calendar, tasks, and notes) is migrated to the target (destination tenant). After successful migration, the source mailbox is deleted. This means that after the migration, under no circumstances, is the source mailbox available, discoverable, or accessible in the source tenant.

If you are interested in previewing our new feature Domain Sharing for email alongside your cross-tenant mailbox migrations, please complete the form at Domain sharing for email enables users in separate Microsoft 365 tenants to send and receive email using addresses from the same custom domain. The feature is intended to solve scenarios where users in separate tenants need to represent a common corporate brand in their email addresses. The current preview supports sharing domains indefinitely and shared domains during cross-tenant mailbox migration coexistence.

Additionally, at least one mail-enabled security group in the source tenant is required. These groups are used to scope the list of mailboxes that can move from source (or sometimes referred to as resource) tenant to the target tenant. This allows the source tenant admin to restrict or scope the specific set of mailboxes that need to be moved, preventing unintended users from being migrated. Nested groups aren't supported.

You'll also need to communicate with your trusted partner company (with whom you will be moving mailboxes) to obtain their Microsoft 365 tenant ID. This tenant ID is used in the Organization Relationship DomainName field.

To obtain the tenant ID of a subscription, sign in to the Microsoft 365 admin center and go to _AAD_IAM/ActiveDirectoryMenuBlade/Properties. Click the copy icon for the Tenant ID property to copy it to the clipboard.

You must configure the target (destination) first. To complete these steps, you are not required to have or know the tenant admin credentials for both source and target tenant. Steps can be performed individually for each tenant by different administrators.

On the "Register an application page", under "Supported account types", select" Accounts in any organizational directory (Any Azure AD directory - Multitenant)". Then, under "Redirect URI (optional)", select Web and enter Lastly, select Register.

Formulate the URL to send to your trusted partner (source tenant admin) so they can also accept the application to enable mailbox migration. Here's an example of the URL to provide to them you'll need the application ID of the app you created:

You will need the application ID of the mailbox migration app you just created and the password (the secret) you configured during this process. Also depending on the Microsoft 365 Cloud Instance you use your endpoint may be different. Please refer to the Microsoft 365 endpoints page and select the correct instance for your tenant and review the Exchange Online Optimize Required address and replace as appropriate.

You will need the application ID of the mailbox migration app you just created.You will need to replace in the above example with your source tenants correct name.You will also need to replace [application_id_of_the_app_you_just_created] with the application ID of the mailbox migration app you just created.

The tenant ID that you enter as the $sourceTenantId and $targetTenantId is the GUID and not the tenant domain name. For an example of a tenant ID and information about finding your tenant ID, see Find your Microsoft 365 tenant ID.

You can verify cross-tenant mailbox migration configuration by running the Test-MigrationServerAvailability cmdlet against the cross-tenant migration endpoint that you created on your target tenant.Run the following cmdlet from target tenant:

If a mailbox is required to move back to the original source tenant, the same set of steps and scripts will need to be run in both new source and new target tenants. The existing Organization Relationship object will be updated or appended, not recreated. The migration can't happen both ways simultaneously.

Users migrating must be present in the target tenant and Exchange Online system (as MailUsers) marked with specific attributes to enable the cross-tenant moves. The system will fail moves for users that aren't properly set up in the target tenant. The following section details the MailUser object requirements for the target tenant.

Microsoft is developing a feature to provide a secure automated method to set many of the attributes in the following section. This feature, named Cross-Tenant Identity Mapping, is currently looking for customers willing to participate in a small private preview. For more information about this pre-release feature and how it can simplify your cross-tenant migration processes, see the article Cross-Tenant Identity Mapping.

Non-hybrid target tenants can modify the quota on the Recoverable Items folder for the MailUsers prior to migration by running the following command to enable Litigation Hold on the target MailUser object and increasing the quota to 100 GB:

Cross-tenant Exchange mailbox migrations are initiated from the target tenant as migration batches. This is like the way that on-boarding migration batches work when migrating from Exchange on-premises to Microsoft 365.

Yes, you should update the targetAddress (RemoteRoutingAddress/ExternalEmailAddress) of the source on-premises users when the source tenant mailbox moves to target tenant. While mail routing can follow the referrals across multiple mail users with different targetAddresses, Free/Busy lookups for mail users MUST target the location of the mailbox user. Free/Busy lookups will not chase multiple redirects.

The meetings will move, however the Teams meeting URL does not update when items migrate cross-tenant. Since the URL will be invalid in the target tenant, you will need to remove and recreate the Teams meetings.

No, the Teams chat folder content does not migrate cross-tenant. When a mailbox is migrated cross-tenant with this feature, only user visible content in the mailbox (email, contacts, calendar, tasks, and notes) is migrated.

Since only one tenant can own a domain, the former primary SMTPAddress will not be associated to the user in the target tenant when the mailbox move completes; only those domains associated with the new tenant. Outlook uses the user's new UPN to authenticate to the service and the Outlook profile expects to find the legacy primary SMTPAddress to match the mailbox in the target system. Since the legacy address is not in the target System the outlook profile will not connect to find the newly moved mailbox.

The first role is for a one-time setup task that establishes the authorization of moving content into or out of your tenant/organizational boundary. As moving data out of your organizational control is a critical concern for all companies, we opted for the highest assigned role of Organization Administrator (OrgAdmin). This role must alter or set up a new OrganizationRelationship that defines the -MailboxMoveCapability with the remote organization. Only the OrgAdmin can alter the MailboxMoveCapability setting, while other attributes on the OrganizationRelationship can be managed by the Federated Sharing administrator.

Cross-Tenant mail flow after migration works similar to Exchange Hybrid mail flow. Each migrated mailbox needs the source MailUser with the correct targetaddress to forward incoming mail from source tenant to mailboxes in target tenant. Transport rules, security and compliance features will run as configured in each tenant that the mail flows through. So, for inbound mail, features like anti-spam, anti-malware, quarantine, as well as transport rules and journaling rules will run in the source tenant first, then in the target tenant.

Mailbox Permissions that are stored in the mailbox will move with the mailbox when both the principal and the delegate are moved to the target system. For example, the user TestUser7 is granted FullAccess to the mailbox TestUser_8 in the tenant After the mailbox move completes to, the same permissions are set up in the target directory. Examples using _Get-MailboxPermission for TestUser_7 in both source and target tenants are shown below. Exchange cmdlets are prefixed with source and target accordingly.

Cross-tenant mailbox and calendar permissions are NOT supported. You must organize principals and delegates into consolidated move batches so that these connected mailboxes are transitioned at the same time from the source tenant.

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