Published November 12, 2026
What the job is
A tenant-to-tenant migration moves users and their data from one Microsoft 365 tenant to another. Microsoft lists four business reasons: a merger or acquisition, a divestiture or spin-off, consolidation of tenants left by past acquisitions, and internal reorganization.
Microsoft has a native tool for each of mailboxes, OneDrive, SharePoint sites, and Teams chats and meetings. Cross-tenant mailbox migration moves Exchange Online mailboxes. Cross-tenant OneDrive migration moves OneDrive accounts. Cross-tenant SharePoint migration moves sites. Migration Orchestrator runs mailboxes, OneDrive, Teams chats and Teams meetings together in one batch.
The tools move content, not identities. The target tenant's users, groups and licenses must be built and configured correctly before any data moves.
One cutover or phased
Microsoft's Migration Orchestrator documentation describes three models. A single-event migration moves all users and workloads in one cutover. A phased migration moves users in batches over time. A tenant move or split moves a subset of users to a new tenant while others stay. Microsoft calls the last one common in divestitures.
A phased migration means a period of coexistence. Microsoft's planning guidance names three things to run during it: mail routing between tenants, calendar free/busy sharing, and Teams federation.
The second decision is the domain. Only one tenant can own a domain. Users either take a new address and sign-in name in the target, or the old domain moves to the target once nothing in the source uses it.
Microsoft's tools and what they move
| Tool | What it moves | License |
|---|---|---|
| Cross-tenant mailbox migration | Email, contacts, calendar, tasks, notes and Recoverable Items. Run from the target tenant as migration batches. | Cross Tenant User Data Migration, per user, one-time fee |
| Cross-tenant OneDrive migration | OneDrive accounts, up to 5 TB or 1 million items each. Leaves a redirect at the source. | Cross Tenant User Data Migration (the same license covers mailbox and OneDrive) |
| Cross-tenant SharePoint migration | Group-connected, modern, classic and communication sites, up to 5 TB or 1 million items each. Leaves a redirect at the source. | Cross-Tenant Shared Data Migration, per 100 GB moved, Enterprise Agreement customers only |
| Migration Orchestrator | Mailboxes, OneDrive, Teams chats and Teams meetings for each user, sequenced in one batch. | Cross Tenant User Data Migration |
| Cross-Tenant Identity Mapping | No content. Maps source users to target users and writes the attributes migration needs. | None stated |
Microsoft's tools do not move teams and channels. Migration Orchestrator leaves shared data such as teams, channels and SharePoint sites in the source. Moving a Teams-connected site with cross-tenant SharePoint migration moves only the site content. Microsoft lists partner and third-party tools as the third option.
The order of the work
- Inventory the source. Count users, mailbox and archive sizes, OneDrive and site storage, holds, sensitivity labels, flows and site customizations.
- Decide identity and domains. Settle whether users keep their sign-in names, and when each domain moves.
- Buy the licenses. Migrations fail without a Cross Tenant User Data Migration license on the source or target user. Microsoft offers no exceptions.
- Build the target. Create users as mail users, not mailboxes, and block OneDrive creation for them. A user who already has a mailbox or OneDrive in the target causes the migration to fail.
- Run identity mapping. Cross-Tenant Identity Mapping writes ExchangeGUID, ArchiveGUID, LegacyExchangeDN as an X.500 address, and the source X.500 proxy addresses onto each target mail user. Run it before assigning workload licenses such as E5 in the target.
- Set up trust. Configure the organization relationship, migration endpoint and mail-enabled security groups that scope who may move. Orchestrated Teams migration also needs its migration apps enabled in both tenants.
- Pilot, then migrate in batches. Microsoft recommends no more than 2,000 mailboxes per batch, submitted at least two weeks before cutover. OneDrive and SharePoint share a queue of 4,000 pending moves.
- Clean up the source. Convert leftover mail users to contacts or remove them, retire redirects when ready, and move the domains.
What takes longer than expected
- Holds. Mailboxes on any type of hold do not migrate. OneDrive accounts with a hold policy are blocked until the hold is removed, then the hold is reapplied in the target. Get legal sign-off before removing any hold.
- Target object hygiene. A target mail user with an SMTP address from a domain the target does not own blocks the move. A license applied before ExchangeGUID is stamped creates a new, empty mailbox instead.
- Mailboxes near quota. They can fail. Reduce their size, or add an archive or auto-expanding archive, before the move. Users with more than 12 auxiliary archive mailboxes cannot move.
- Path length. Source paths plus the new OneDrive or site URL must stay within 400 characters. Usernames or URLs with an apostrophe fail.
- Validation. Microsoft says some Migration Orchestrator batches need multiple rounds of review and correction to pass validation, and tells admins to plan validation as active work.
What plans leave out
- Outlook profiles. After the move, users rebuild their profile with the new sign-in name and resync the offline file. Plan network capacity for those downloads.
- Teams meetings moved by mailbox migration keep invalid join links and must be recreated.
- Mailbox and calendar permissions do not carry across tenants. Delegates and the mailboxes they use must move in the same batch.
- Signatures, Outbox items and the Teams chat folder in the mailbox do not migrate.
- Sensitivity labels are not exported. Recreate them in the target. On SharePoint, files with labels using user-defined permissions must be unlabeled before the site can move.
- SharePoint 2010 and 2013 workflows, apps, Power Apps and Power Automate flows must be recreated or republished in the target.
- Customer Key service encryption on the source causes OneDrive and SharePoint migrations to fail.
Licensing, cost and compliance
The Cross Tenant User Data Migration add-on is a one-time fee per user, assigned in either tenant. It is an add-on to Microsoft 365, Office 365, Exchange Online, SharePoint, OneDrive and EDU plans. Migration Orchestrator's documentation lists it for EA, CSP, web direct, small business and EDU customers.
SharePoint sites need a separate license. Cross-Tenant Shared Data Migration is sold per 100 GB moved, to Enterprise Agreement customers only. Microsoft allows 20 percent grace above measured storage.
Budget for workload licenses in both tenants during the project. Target users need an Exchange Online license for mailbox migration. Orchestrated Teams chat migration requires a Teams license in both tenants, and Teams meetings migration requires an Exchange Online license in both.
eDiscovery stops in the source once a mailbox moves, because the source mailbox is deleted. If the source company must keep a searchable copy, copy the mailbox before migration. Microsoft tells regulated organizations to consult legal and compliance teams first.
Skills and operations
The native tools run largely from Exchange Online PowerShell, SharePoint Online PowerShell and Microsoft Graph. Mailbox batches can also be submitted from the Exchange admin center. The team needs people who can script against all three.
Two tenants means two sets of administrators. Setting up the mailbox move relationship needs the Exchange Organization Administrator role. Running moves can be delegated to the Move Mailboxes role. Granting Cross-Tenant Identity Mapping its permissions needs a Global Administrator in each tenant.
Settle these first
- Which domains move, and on what date can nothing in the source still use them?
- Which mailboxes and OneDrive accounts are on hold, and has legal approved the plan for each?
- How many users need the per-user license, and how many 100 GB units do the SharePoint sites need?
- How will teams, channels and their chats be rebuilt, since Microsoft's tools do not move them?
- Who holds Global Administrator and Exchange Organization Administrator in each tenant during the project?
- How long will the source tenant stay licensed for redirects, eDiscovery and coexistence?
Questions
- Does Microsoft have a native tenant-to-tenant migration tool?
- Yes. Microsoft provides cross-tenant mailbox, OneDrive and SharePoint migration, and Migration Orchestrator for mailboxes, OneDrive, Teams chats and meetings together. None of them moves teams and channels.
- What license is needed for a cross-tenant migration?
- Each migrating user needs a Cross Tenant User Data Migration license, a one-time fee per user, assigned in either tenant. It covers mailbox and OneDrive. SharePoint sites need Cross-Tenant Shared Data Migration, sold per 100 GB to Enterprise Agreement customers.
- Can we run a delta pass after a OneDrive or SharePoint move?
- No. Microsoft describes cross-tenant OneDrive and SharePoint moves as one-time. Content moves, a redirect stays at the source, and incremental or delta passes are not possible.
- Can both tenants use the same email domain during the migration?
- No. A domain belongs to one tenant at a time. The source and target must use different domains until the domain is removed from the source and added to the target.
- Can we migrate from a commercial tenant to a government cloud tenant?
- No. Microsoft does not support cross-cloud tenant-to-tenant migration, for example from Office 365 Worldwide to Office 365 Government. Cross-tenant OneDrive migration is not supported for GCC, GCC High or DoD users.