Tenant-to-tenant consolidation of two Microsoft 365 tenants

The problem

Two separate Entra ID and Microsoft 365 tenants had to become one, without users losing mail, files or access, and without every device having to be registered again.

What I did

I covered the whole life of the migration: discovery, design, cutover, rollback, communications and validation.

• Discovery listed users, mailboxes, sites, OneDrive data, Intune devices and policies.
• The design kept the existing domain names, so users did not need to re-register devices.
• The cutover plan had a rollback path and a go or no-go point before anything hard to undo.
• Communications told users what to do before, during and after each stage.
• Validation checked each user and device against the same list.

The result

Over 1,000 mailboxes, SharePoint Online, OneDrive and over 500 Intune devices moved into one tenant. Users kept their domain names and did not re-register devices.

The approach is described in Planning a Microsoft 365 tenant-to-tenant migration.