Microsoft 365 tenant-to-tenant migration checklist (35 steps)

Scope and plan

• Agree the scope for each workloadList mail, OneDrive, SharePoint, Teams, Power Platform and devices separately, because each moves with a different method.
• Decide how identities map between tenantsMicrosoft's planning guide asks you to decide whether users keep their existing UPN or receive a new one.
• Decide whether you need coexistenceFor a phased move, plan mail routing, calendar free/busy sharing and Teams federation between the two tenants.
• Plan when each custom domain movesMicrosoft's planning guide says to plan for any domain transfers between tenants. Put the domain move in the cutover runsheet.
• Pick a tool for each workloadMicrosoft's native cross-tenant tools cover mailboxes, OneDrive and SharePoint. They do not move Teams channels or chats.
• Set the order of workloadsMicrosoft notes Teams content depends on Exchange mailboxes, and OneDrive and SharePoint share a permissions model, so move them together.

Licensing and blockers

• Buy Cross-Tenant User Data Migration licencesMailbox and OneDrive moves need this per-user add-on. Microsoft says migrations fail without it and offers no exceptions.
• Check SharePoint cross-tenant eligibilityMicrosoft's built-in tenant-to-tenant SharePoint site move needs the Cross-Tenant Shared Data Migration licence, which Microsoft currently sells only to Enterprise Agreement customers. An Enterprise Agreement is a volume licensing contract Microsoft signs directly with large organisations; most small and medium businesses buy Microsoft 365 through a reseller or online instead, cannot buy this licence, and use a third-party tool for SharePoint sites.
• Confirm target licences are availableMake sure the target tenant has enough licences for every user before the first batch.
• Find mailboxes and OneDrive accounts on holdAccounts on any hold are blocked. Remove the hold, migrate, then reapply the policy in the target.
• Check Customer Key on the source tenantCross-tenant OneDrive migration fails if Microsoft Purview Customer Key service encryption is enabled on the source.
• Check for government cloud usersMicrosoft says cross-tenant OneDrive migration is not supported for GCC, GCC High or DoD users.

Prepare the target tenant

• Precreate users and groups in the targetCreate and license accounts first so permissions can be mapped.
• Stop OneDrive sites being created earlyIf the target OneDrive already exists the migration fails and cannot overwrite it.
• Build and check the identity mapping fileUsernames or URLs that contain an apostrophe fail with an invalid character error.
• Create a mail-enabled security group in the sourceThis group limits which mailboxes can move. Use more than one group for over 10,000 users.
• Stamp target MailUsers with source attributesCopy ExchangeGUID, ArchiveGUID and the LegacyExchangeDN as an x500 address, plus all other x500 addresses.
• License the Exchange plan only after ExchangeGUID is setMicrosoft warns that licensing first creates a new mailbox instead of a MailUser ready to receive the move.

Set up trust and endpoints

• Register the migration app in the targetAdd the Office 365 Exchange Online Mailbox.Migration application permission and copy the client secret straight away.
• Have the source admin grant consentSend the source admin the admin consent URL for the app.
• Create both organisation relationshipsInbound on the target, RemoteOutbound on the source, scoped to the mail-enabled security group.
• Create and test the migration endpointRun Test-MigrationServerAvailability against the endpoint before you create a batch.
• Establish and verify SharePoint trustAdmins in both tenants run Set-SPOCrossTenantRelationship, then verify trust before scheduling OneDrive moves.

Migrate

• Run a pilot batchMove a small group of test users and check mail, calendar and OneDrive access end to end.
• Keep each mailbox batch to 2,000 users or fewerMicrosoft says not to exceed 2,000 mailboxes per batch. Use target-tenant addresses in the CSV.
• Move delegates with their principalsCross-tenant mailbox and calendar permissions are not supported, so keep them in the same batch.
• Queue OneDrive moves within the limitUp to 4,000 OneDrive accounts can be scheduled in advance at one time per source.
• Treat OneDrive and SharePoint moves as one passMicrosoft says cross-tenant moves cannot run incremental or delta passes.
• Move Teams with a third-party toolTeams chat folder content is not migrated by the mailbox move, and SharePoint moves do not include Teams channels.

Cutover and clean-up

• Recreate Teams meetingsTeams meeting URLs are not updated by the mailbox move.
• Restamp Send on Behalf and recreate signaturesMicrosoft lists both as not migrated.
• Move the custom domain and update DNSFollow the domain steps in your cutover runsheet.
• Turn Power Automate flows back onAfter a Power Platform environment move, flows are off by default and HTTP trigger URLs change.
• Export anything you must keep from the source firstAfter a successful move the source mailbox is deleted and cannot be searched in the source tenant.
• Remove endpoints and organisation relationshipsUse Remove-MigrationEndpoint and Remove-OrganizationRelationship once all batches are complete.

Official sources