This guide is part of our M365 Migration Series.
Explore every step of the tenant-to-tenant migration journey below:
Mergers and acquisitions often bring the challenge of consolidating multiple M365 tenants into a single environment. This is a common scenario in larger organizations transitioning through IT Services Mergers and Acquisitions,
While migrating Exchange and Teams usually gets a lot of attention, SharePoint and OneDrive for Business (OD4B) are equally critical, sense they house collaboration sites, departmental knowledge, and personal files that your clients rely on daily.
This blog walks through a high-level strategy for migrating SharePoint and OD4B content from one M365 tenant to another, while using Microsoft-native tools as much as possible to cut down on migration costs. We’ll also highlight where third-party solutions may provide additional value for your organization.
Step 1: Pre-Migration Planning
Every successful migration starts with knowing your environment. Before starting any SharePoint migration, be sure to:
- Inventory: catalog the SharePoint site collections, subsites, and OneDrive accounts in the acquired tenant. Document, as much as possible, storage quotas, permissions, external sharing links, and customizations.
- Take special care to inventory any item (site, folder, or file) that has external sharing links enabled. These do NOT migrate in a tenant-to-tenant migration and will need to be recreated post-migration. See Step 6: External Sharing Links for more information.
- Prioritization: identify business-critical sites and OneDrive accounts that must be migrated first. For example, HR and Finance sites often need to be available with minimal downtime during a merger to make sure the merger is completed on schedule.
- Governance & Compliance: document retention policies, sensitivity labels, and DLP rules in the acquired tenant. Ensure that compliance teams sign off on the migration plan, especially if regulated data is involved.
- Communication: Draft end-user communication templates. You should pay particular attention to drafting clear instructions for users to reconfigure the OneDrive sync client.
Step 2: Tenant Preparation
Before moving a single file, the acquiring tenant must be ready.
- SharePoint Configuration: align site creation policies, external sharing settings, and storage quotas with the new organization’s standards.
- Be prepared to address any of these that are different in the acquiring tenant.
- For example, if standard OneDrive quotas are smaller in the acquiring tenant, be prepared to address that with clients being acquired.
- OneDrive Provisioning: make sure that OneDrive accounts exist in the acquiring tenant for all users that are being migrated.
- Identity Mapping: plan Entra ID user mapping. If UPNs are changing (e.g., @companyA.com → @companyB.com), document the mapping strategy.
- If you’re doing SharePoint before Exchange, keep in mind that UPNs also matter for Exchange. Don’t make a decision here in isolation that will affect the Exchange migration.
- Licensing Alignment: confirm that both tenants have the necessary licenses to support the combined SharePoint and OneDrive workloads.
Step 3: Migration Strategy
Microsoft-Native Tools
- SharePoint Migration Tool (SPMT): ideal for moving document libraries and site content. SPMT supports incremental migrations and preserves file/folder metadata.
- Mover (Microsoft-acquired service): built for OneDrive migrations. Mover handles bulk user migrations with some reporting and error handling.
- PowerShell & Graph API: useful for scripting user mappings, permissions, and reporting.
When Third-Party Tools May Be Better
- Complex Permissions: tools like BitTitan, ShareGate, and Quest can handle nuanced permission mapping and reporting more gracefully.
- Large-Scale Migrations: third-party tools often provide dashboards, throttling management, and retry logic that is better than native tools.
- Coexistence Scenarios: if users need to work across both tenants temporarily, third-party solutions can provide smoother coexistence.
Step 4: Migration Execution
As with our recommendations for Exchange Online, start small and gradually build up your migration waves while taking feedback from clients and adjusting along the way.
- Pilot Migration: start small. Select a handful of SharePoint sites (one, maybe two small sites) and OneDrive accounts (two or three) to validate migration performance, metadata preservation, and permission migrations.
- Pilot Migration 2: migrate a 4-5 SharePoint sites and 10-20 OneDrive accounts. You should have one or two not-typical use cases in this wave to identify potential gaps in your migration strategy.
- Bulk Migration: further expand in larger waves – department by department or site by site.
- User Communication: Notify users before their OneDrive cutover takes place. Provide clear instructions for accessing files in the new tenant and reconfiguring sync clients.
Step 5: Post-Migration Validation
Once the migration is complete, validation is critical.
- Data Integrity: verify file counts and permissions match the source tenant.
- User Acceptance Testing: confirm OneDrive sync clients are reconfigured. Validate SharePoint customizations such as workflows and Power Automate flows.
Step 6: External Sharing Links Considerations
One critical component of tenant-to-tenant SharePoint migrations is external sharing links.These migrations often happen as part of broader organizational changes, including IT Services Mergers and Acquisitions, where consolidating environments and aligning collaboration workflows become essential.
These links are tenant-bound, meaning they reference the acquired tenant domain. Once content is migrated, these links break and external collaborators will no longer be able to access files or sites using the old URLs.
To address this:
- Inventory Before Migration: use PowerShell or reporting tools to inventory all external sharing links in the acquired tenant. This gives you visibility into which files and sites are actively shared outside the organization.
- Communicate Early: notify your clients that the existing links will break as part of the migration. Come up with a strategy for them to follow to re-create the links post-migration and share the new links with their external collaborators.
- Recreate Links Post-Migration: after migration, instruct your clients to re-establish external sharing links in the new tenant.
- Governance Opportunity: use this opportunity to audit external sharing practices. It can be a chance to tighten policies, reduce risk, and align external collaboration with compliance standards. Even if policies don’t need to change, you can use this opportunity to potentially remove some external access if it’s no longer required.
Important: Neither Microsoft-native tools (SPMT, Mover) nor third-party platforms (ShareGate, BitTitan, Quest) preserve external sharing links across tenants. They can help you inventory and report on them but manually re-establishing external sharing links is always required.
Step 7: Recommended Strategy
- Phased Migration: start with a pilot, expand in waves, and finalize with cutover. Avoid “big bang” migrations unless absolutely necessary due the complexity of support involved with all users (or most) moving at once.
- Native-First Approach: cut costs by using Microsoft-native tools in straightforward migrations. Introduce third-party tools if scale, complexity, or reporting requirements exceed the Microsoft-native capabilities.
- Continuous Communication: keep users informed throughout the process. Provide quick-start guides for accessing OneDrive and SharePoint in the new tenant.
Conclusion
Tenant-to-tenant migrations in M&A scenarios are complex, but with careful planning, the right tools, and clear communication, they can be executed smoothly. Microsoft-native tools like SPMT and Mover provide a solid foundation, while third-party solutions can fill gaps in scale, reporting, and coexistence.
By following a thoroughly planned, phased approach, organizations can minimize disruption, maintain compliance, and ensure employees have seamless access to the content they need in the new tenant.
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