Moving users between Microsoft 365 tenants sounds like a copy job. It is closer to moving house while still living in both homes: identities, mail, files, Teams, devices and domains all move on different schedules, and some things can't be moved at all.
What moves cleanly
Mailboxes, including archives, calendars and contacts, move well with Microsoft's cross-tenant mailbox migration or third-party tools. OneDrive content moves well too. SharePoint sites move with their content and, with planning, their permissions. Groups and distribution lists can be recreated and repopulated with scripts.
What needs more work
Teams is the hardest workload. Channel files live in SharePoint and move with the site, but channel conversations, private chats and meeting recordings need third-party tooling, and even then the result isn't identical. Plan what people need to keep, and archive the rest.
Permissions need mapping. Every permission references an identity in the old tenant, so each one has to be translated to the matching identity in the new one. Sharing links created in the old tenant stop working.
What doesn't move
Devices don't move between tenants. Entra-joined devices have to be reset or unjoined and rejoined, and Autopilot registrations must be deleted from the old tenant and imported into the new one. Licences don't transfer either; the target tenant needs its own. Audit logs and some compliance records stay behind, which matters if you are under legal hold.
What breaks on the day
The domain. A domain can only be verified in one tenant at a time, so it has to be removed from every object in the old tenant before it can be added to the new one. That creates a cutover window that needs mail routing planned to the hour.
Links and integrations. Teams meeting links, bookmarks to SharePoint, single sign-on apps, scanners that email documents and line-of-business apps that send mail all point at the old tenant. Find them in discovery, not on Monday morning.
How to keep it under control
Start with coexistence, so people can meet and chat across tenants while the migration runs. Move a pilot group end to end. Migrate in waves that keep teams together. Pre-stage data so each cutover is short. And keep the old tenant until retention and legal obligations are met.
Planning a tenant migration? Tenant-to-tenant migration
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