Why tenant migrations are special
Unlike a pure mailbox move, a tenant consolidation affects an organisation’s entire digital identity: user accounts, primary email domains, groups, shared mailboxes, Teams, SharePoint sites and OneDrive data. In addition, a domain can only ever be active in one tenant. That makes the order of the steps critical.
The process at a glance
1. Inventory of both tenants
Users, licences, domains, groups, shared mailboxes, Teams and SharePoint content are recorded on both sides and mapped to each other.
2. Resolve naming conflicts
Duplicate display names, identical alias addresses or colliding group names are resolved before the migration.
3. Pre-migration of the content
Mailboxes, OneDrive and SharePoint data are transferred to the target tenant while both environments are still in production.
4. Coordinated cut-over
The domain is released in the source tenant and activated in the target tenant, and the MX records are switched. This step is tightly scheduled to minimise downtime.
5. Delta and follow-up
New content is transferred afterwards, permissions are checked, and forwarding and signatures are set up.
Typical challenges
- Releasing the domain: detaching a domain from the old tenant can take some time; this must be built into the schedule.
- Identities: with a hybrid setup (Entra ID / Active Directory), synchronisation needs careful planning.
- Teams & SharePoint: content, memberships and permissions are more complex than plain mailboxes.
- Transition phase: as long as both tenants exist, addressing between them should work (mail routing) so that internal communication does not break off.
What matters in the project
Tenant migrations depend on planning and coordination. A dedicated contact, an agreed cut-over date and object-level validation matter more here than in any other type of migration. We move all content via our own servers in Germany and the EU and document completeness after the project.
Frequently asked questions
Can a domain be active in both tenants at the same time?
No. A domain can only be active in one Microsoft 365 tenant at a time. That is why the order (release first, then activate in the target) is decisive and tightly scheduled.
How do we prevent internal emails from getting lost during the switch?
With a transition phase with coordinated mail routing between the tenants and a delta migration that transfers messages received in the meantime.
What does a tenant-to-tenant migration cost?
The project fee is 200 € per project, plus per mailbox 29 € for emails including folders, 5 € each for calendars and contacts and 19 € for OneDrive files (up to 50 GB per user). For 50 mailboxes with all four components that comes to 2,810 € net, because from 50 mailboxes a 10 % volume discount applies to the mailbox total. SharePoint sites, Teams files and shared mailboxes are priced according to effort.
How long does a tenant-to-tenant migration take?
Most of the data is transferred in the background beforehand while both tenants keep running normally. It only gets tight at the domain switch: the release in the old tenant and the activation in the new one take place in a scheduled window, usually at the weekend. Small environments are switched over in a few days; for larger ones, expect one to several weeks of lead time.