Plan a Microsoft 365 tenant-to-tenant migration

There are several architecture approaches for mergers, acquisitions, divestitures, and other scenarios that might lead you to migrate an existing Microsoft 365 tenant to a new tenant. This article helps you understand the planning considerations and choose the right approach.

Common scenarios

Tenant-to-tenant migrations typically occur in one of the following business contexts:

  • Merger or acquisition: Your organization acquired another company, and you need to consolidate users and data into a single tenant.
  • Divestiture or spin-off: A business unit is being separated, and users need to move to a new or existing tenant owned by another organization.
  • Consolidation: Your organization has multiple tenants from past acquisitions and wants to consolidate into one.
  • Internal reorganization: Business restructuring requires moving users between tenants within the same parent organization.

Choose your migration approach

Your approach depends on the scope of the migration and the workloads involved.

Approach Best for Tool
Multi-workload orchestrated migration Migrating mailboxes, OneDrive, SharePoint, and Teams together in coordinated batches Migration Orchestrator
Individual workload migration Migrating a single workload, or when you need granular control over each workload's timeline Cross-tenant tools (mailbox, OneDrive, SharePoint)
Partner or third-party tools Complex migrations requiring specialized capabilities, or when internal resources are limited Microsoft Consulting Services or certified partner tools

Key planning considerations

Before you start a migration, consider the following areas:

Identity strategy

  • Decide how user identities map from the source tenant to the target tenant. For more information, see Cross-tenant identity mapping.
  • Determine whether users keep their existing UPN or receive a new one.
  • Plan for any domain transfers between tenants.

Workload dependencies

Workloads have dependencies that affect migration sequencing:

  • Teams content depends on Exchange mailboxes: Migrate mailboxes before or alongside Teams.
  • OneDrive and SharePoint share permissions models: Consider migrating them together.
  • The Migration Orchestrator handles sequencing automatically for supported workloads.

Coexistence during migration

For phased migrations, plan for a period where users exist in both tenants:

  • Mail routing between tenants during the transition.
  • Calendar free/busy sharing between source and target.
  • Teams federation for cross-tenant communication.

Licensing

  • Make sure you have sufficient licenses available in the target tenant before migration.
  • Migration Orchestrator requires specific licensing. For details, see Planning and prerequisites.

Timeline estimation

Migration throughput depends on data volume, workload type, and batch size. Factors that affect your timeline include:

  • Number of users and mailbox sizes.
  • Volume of OneDrive and SharePoint content.
  • Any mailboxes on hold (which might block migration).
  • Network bandwidth between tenants and Microsoft 365 services.

Next steps

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