How do you migrate from one Microsoft 365 tenant to another?
A Microsoft 365 tenant-to-tenant migration moves users, mailboxes, OneDrive and SharePoint content, Teams and domains from one tenant to another, typically after an acquisition, divestiture or rebrand. It is done with Microsoft's cross-tenant migration features or third-party tools, and succeeds or fails on planning: identity mapping, licensing, domain cutover, permissions and user communication.
Why companies migrate tenants
Common reasons are mergers and acquisitions, divestitures that need a clean separation, consolidating several tenants after growth, and moving to a government cloud for compliance. Each has different constraints, especially around timing and who controls the source tenant.
What moves, and what needs rebuilding
- Mailboxes, calendars and contacts
- OneDrive files
- SharePoint sites and Teams content, which often require third-party tools or rebuild
- Domains and email addresses, which can only be verified in one tenant at a time
- Identities, groups and permissions, which must be mapped carefully
- Security settings, Conditional Access policies, devices and app registrations, which usually need re-creating in the target
Microsoft's native cross-tenant tools
Microsoft supports cross-tenant mailbox migration and cross-tenant OneDrive migration. Microsoft's documentation states these require a per-user Cross Tenant User Data Migration license, a one-time fee per user assigned on the source or target user, and that migrations fail without it. The license covers both mailbox and OneDrive migration.
Microsoft also states that cross-cloud tenant-to-tenant migration is not supported, giving the example of moving from Office 365 worldwide to an Office 365 government cloud. A move into GCC High therefore needs a different approach, which is a common surprise for defense suppliers.
A sound plan
- Inventory both tenants: users, mailboxes, sites, Teams, licenses, apps and integrations
- Decide the target identity design and how users and groups map across
- Confirm licensing in the target, including any migration licenses
- Pilot with a small group, then migrate in waves
- Plan the domain cutover window and DNS changes
- Rebuild security baselines and Conditional Access in the target before users arrive
- Communicate early, with clear instructions for re-signing into Outlook, Teams and mobile devices
Do not forget the old tenant
Before decommissioning the source tenant, confirm what must be retained for legal, regulatory or contractual reasons and how it will be preserved. Back up anything you may need later; once the old tenant is gone, recovery options end.
Common pitfalls are predictable: starting the data move before identity mapping and licensing are settled, forgetting third-party apps that authenticate against the old tenant, leaving security baselines unbuilt in the target, and underestimating the support load on cutover day. A pilot wave surfaces most of these early, when they are cheap to fix.
Common follow-up questions
How long does a tenant-to-tenant migration take?
It depends on the number of users, data volume, SharePoint and Teams complexity, and how many integrations must be rebuilt. Discovery and planning often take longer than the data move itself. Pilot first to measure real throughput before committing to cutover dates.
Can users keep their email addresses?
Yes, but a domain can only be verified in one tenant at a time, so the domain must be removed from the source and added to the target during a planned cutover window. Plan DNS changes and mail flow carefully to avoid lost or delayed email.
Can we migrate from commercial Microsoft 365 to GCC High with the native tools?
Microsoft states that cross-cloud tenant-to-tenant migration is not supported by its cross-tenant mailbox migration feature. Moves into a government cloud need separate planning and tooling, and should be scoped alongside your compliance requirements.
LAN Service Group plans and executes Microsoft 365 migrations for small and mid-size businesses, including Microsoft 365 GCC High migration and administration for defense suppliers.
Talk to LAN Service Group (888) 281-7243