A tenant-to-tenant migration moves users, email, files, and Teams data from one Microsoft 365 organization to another. It's common after an acquisition, a merger, a divestiture, or when a business is consolidating separate tenants.
The domain constraint
A custom domain can only be verified in one Microsoft 365 tenant at a time. If users need to keep their existing email addresses, the domain has to be removed from the old tenant before it's added to the new one. That step drives much of the cutover planning.
A typical sequence
- Discovery: inventory users, shared mailboxes, groups, SharePoint sites, Teams, and the applications connected to the tenant.
- Preparation: create accounts and licenses in the destination tenant and plan how identities map between them.
- Pre-staging: copy most mailbox and file data ahead of time while people keep working.
- Cutover: move the domain, switch mail delivery, run a final data sync, and update sign-in for users, typically over a weekend.
- Follow-up: reconnect Outlook and OneDrive on each device, fix permissions, and support users through the first days.
What users will notice
Even with good planning, users usually need to sign in again, may need to reconfigure mobile devices, and may find some links to old shared files no longer work. Clear communication before the cutover makes the biggest difference to how smooth it feels.
Plan for what doesn't migrate cleanly
Some items, such as certain Teams chat history, app integrations, and device enrollments, may need extra tools or manual work. Identifying these during discovery avoids surprises during the cutover weekend.
Founder of Albano Tech, providing managed IT, Microsoft 365, and cybersecurity services to businesses in Delaware, Maryland, and the Philadelphia region. More about Zach.
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Albano Tech provides Microsoft 365 Management & Migrations for businesses in Delaware, Maryland, and the Philadelphia region.