Microsoft has a native way to move Exchange Online mailboxes between tenants. It needs a per-user license, an app in both tenants and a MailUser for every person. Learn what moves, what stays behind and the 6 setup steps in the order Microsoft gives them, before you plan a cutover.
Email is the first thing users miss after a tenant move. Nobody cares about SharePoint if Outlook is empty on Monday.
I plan the mailbox move first on almost every project. This guide shows how Exchange Online mailbox migration between tenants works, using Microsoft's own page, and where the native route stops.
How does Exchange Online Mailbox Migration Between Tenants Work?
Microsoft's page on cross-tenant mailbox migration describes a move between two Exchange Online organizations. You set up the target tenant first. Both admins then finish their own steps.
The move creates the mailbox in the target tenant, and the source mailbox is deleted after a successful move. The source mailbox becomes a MailUser that points to the target tenant. So there is no quick way back once a batch completes.
What Moves and What Stays Behind in a Mailbox Migration?
Microsoft lists both sides. Check this table before you promise anything to users.
| Group | Items |
|---|---|
| Moves | Email, contacts, calendar, tasks, notes, Recoverable Items, voicemail and greetings |
| Moves with conditions | Mailbox permissions when the principal and delegate move together, shared mailboxes with store permissions only |
| You recreate | Signatures, Teams meeting URLs, labels, Send on Behalf delegates |
| Does not move | Outbox items, Teams chat folder content, Microsoft 365 Groups, SharePoint and OneDrive documents |
What are the Limits of the Native Mailbox Route?
Microsoft's route works, but it asks a lot from admins. Every user needs a Cross-Tenant User Data Migration license. It is a per-user, one-time fee that Microsoft says must be in place before you start. Migrations fail without it, and Microsoft offers no exceptions.
Mailboxes on any hold are blocked from moving. Mailboxes that exceed the target tenant's quota fail. Mailboxes with more than 12 auxiliary archives are not supported, and cross-cloud moves, like Worldwide to GCC, are not supported either. Source and target domain names must be unique.
Setup is also PowerShell heavy. If your team does not use Exchange Online PowerShell every week, plan time for practice and a pilot.
How do You Migrate Exchange Online Mailboxes Between Tenants?
These are the steps in the order Microsoft gives them. Always follow the live page, because Microsoft can change details.
- Buy licenses and scope users. Verify the Cross-Tenant User Data Migration licenses. In the source tenant, create a mail-enabled security group that scopes which mailboxes can move, and get the partner's tenant ID.
- Register the app in the target tenant. In the Microsoft Entra admin center, create a multi-tenant app with the Exchange Online application permission Mailbox.Migration. Create a client secret and save it right away, because it shows only once. Then grant admin consent.
- Create the endpoint in the target tenant. In Exchange Online PowerShell, use New-MigrationEndpoint and New-OrganizationRelationship with MailboxMoveCapability set to Inbound.
- Accept consent in the source tenant. The source admin accepts the app, then sets the organization relationship with MailboxMoveCapability RemoteOutbound and the scope group.
- Create MailUsers in the target tenant. Match the ExchangeGUID, ArchiveGUID if there is an archive, LegacyExchangeDN as an x500 address and set the primary SMTP and UPN to the new domain. Do not license the MailUser until the ExchangeGUID and proxy addresses are set, or a new mailbox is created.
- Test and start a batch. Use Test-MigrationServerAvailability, then New-MigrationBatch with a CSV of target addresses. Keep batches to 2,000 mailboxes or fewer and submit them about two weeks before cutover.
For the wider plan, read Microsoft 365 migration planning checklist. For budget, read Microsoft 365 migration cost breakdown.
What Happens on Day 1 After a Mailbox Migration?
Microsoft says users must rebuild their Outlook profile with the new UPN and primary SMTP address, then resync OST content. Plan network and capacity for profile creation and OST and OAB downloads.
Admins have work too. Update any on-premises MailUsers or remote mailboxes with the new target address. Re-stamp Send on Behalf with Set-Mailbox. Assign Exchange licenses in the target tenant, which Microsoft's FAQ says to do in the 30-day grace period after migration. Finally, remove the endpoints and organization relationships when you are done.
What does the Mailbox Route Leave Out?
Mail is only one workload. Microsoft says SharePoint and OneDrive documents do not move with a mailbox, and the Teams chat folder content stays searchable in the source tenant.
RecoveryTools OneDrive Migrator copies OneDrive for Business between tenants and within the same organization. It keeps original dates, hash checks every file and never overwrites existing files. It leaves behind sharing links, Personal Vault, OneNote notebooks, the recycle bin, retention and legal holds, sync app settings and guests.
RecoveryTools Teams Migrator copies teams and channels with the author, date and reactions, and carries owners, members and guests with roles. It can also save chats to disk per user. For a plan, read how to migrate OneDrive from one tenant to another and how to migrate Microsoft Teams to another tenant.
Move OneDrive Files Alongside Mailboxes
RecoveryTools OneDrive Migrator copies OneDrive for Business between tenants or inside one organization and keeps original dates. It hash checks every file and the source stays read-only. Test one account first, then move the rest.
No credit card, no sign-up. Works on Windows 11, 10 and Windows Server.
What are the Best Practices for Exchange Online Mailbox Migration?
- Pilot a few mailboxes. Test the endpoint, the MailUser match and the Outlook profile rebuild.
- Check holds first. Mailboxes on hold are blocked, so plan the hold change early.
- Submit batches early. Microsoft says to submit about two weeks before cutover, because sync does not affect users.
- Prepare users. Tell people they must rebuild Outlook on day 1.
- Plan documents and chats. Mailbox moves leave OneDrive files and Teams chats behind.
Which Mistakes Break a Mailbox Migration Between Tenants?
Four come up often. First, starting without licenses. Second, licensing the target MailUser too early, which creates a new mailbox. Third, adding users with a hold or an existing move request to a batch. Fourth, forgetting that the source mailbox is deleted after the move.
My Verdict on Exchange Online Mailbox Migration
Microsoft's native route is solid for mail and needs no extra tool. It does ask for licenses, PowerShell skill and careful MailUser setup.
Pilot first, submit batches early and plan OneDrive and Teams separately. Then Monday morning is quiet.
Frequently Asked Questions
Can You Migrate Exchange Online Mailboxes Between Tenants?
Yes. Microsoft documents a cross-tenant mailbox migration between two Exchange Online organizations. It needs a per-user license, an app in both tenants and a MailUser for every person.
What License does a Cross-Tenant Mailbox Migration Need?
Microsoft says every migrated user needs a Cross-Tenant User Data Migration license. It is a per-user, one-time fee that you can assign to the source or target user.
What does Not Move in a Mailbox Migration?
Microsoft lists Outbox items, Teams chat folder content, Microsoft 365 Groups and SharePoint and OneDrive documents. Signatures, labels and Teams meeting URLs must be recreated.
How Big can a Mailbox Migration Batch be?
Microsoft says to keep batches to 2,000 mailboxes or fewer and to submit them about two weeks before cutover. Contact Microsoft for more than 50,000 mailboxes.
What Happens to the Source Mailbox After the Move?
Microsoft says the source mailbox is deleted and converted to a MailUser that points to the target tenant. Plan eDiscovery in the target tenant.
What do Users do on Day 1 After a Mailbox Migration?
Users must rebuild their Outlook profile with the new UPN and primary SMTP address, then resync OST content. Plan network capacity for the downloads.
How do I Move OneDrive Files That a Mailbox Migration Leaves Behind?
Use a separate route. RecoveryTools OneDrive Migrator copies OneDrive for Business between tenants and keeps original dates. Test one account with the free trial first.
Jamie blends strategic marketing insight with technical writing, turning migration and recovery topics into guidance that works for technical and general readers alike.
Published 19 October 2026. Steps, license rules, limits and exclusions come from Microsoft's page on cross-tenant mailbox migration. Product behavior comes from the RecoveryTools OneDrive Migrator and Teams Migrator pages. Microsoft can change these limits, so check them before you plan.