Microsoft 365 Migration Checklist 2026: Complete Enterprise Guide for IT Admins and Migration Teams

What Is an Office 365 Migration Checklist?

A M365 migration checklist is a structured list of tasks for planning, preparing, migrating, and validating data in Microsoft 365. The checklist varies by migration type and may cover Exchange, SharePoint, OneDrive, Teams, or cross-tenant moves. It helps admins verify identities, licenses, workload dependencies, migration limits, and configurations before problems affect the migration.

Follow each and every step of the Microsoft 365 Migration Checklist below.

1. Define Migration Scope and Goals

• Start by documenting exactly what you are moving.
• Identify the source environment and target Microsoft 365 tenant.
• Decide whether the project involves Exchange Online, OneDrive, SharePoint, Teams, or multiple workloads.
• Determine whether this is a new migration to Microsoft 365 or a tenant-to-tenant move.
• Document the reason for migration, such as a merger, acquisition, divestiture, restructuring, or provider change.
• Set the expected migration window and major cutover milestones.
• Identify data that is outside the migration scope.
• Define how migration success will be measured.

For tenant-to-tenant migrations, Microsoft currently describes three broad approaches: individual workload migration, coordinated multi-workload migration using Migration Orchestrator, and partner or third-party tools for more complex requirements.

Do not select the migration method before defining the workloads. The method should follow the project requirements rather than the other way around.

2. Assess Your Existing Environment

Create an inventory before moving anything.

3. Check Identity, Domains, and Users

At this step of the Microsoft 365 migration checklist, you have to check identities. Identity preparation is one of the most important parts of a tenant-to-tenant migration.

• Decide how source users map to target users.
• Determine whether users keep their existing UPN or receive a new one.
• Identify source and target tenant IDs.
• Plan domain transfers separately.
• Precreate required users and groups in the target tenant.
• Remove duplicate or stale identities.
• Map users and groups whose permissions need to be preserved.

For cross-tenant Exchange mailbox migration, Microsoft requires the target user to exist as a MailUser with the required attributes. The target object must be prepared correctly before migration. In particular, the ExchangeGUID must correspond to the source mailbox.

Microsoft also warns that applying an Exchange Online license before the target MailUser is correctly prepared can provision a new mailbox and cause migration problems.

For SharePoint and OneDrive migration, Microsoft similarly requires users and groups identified for migration to be precreated in the target environment.

4. Verify Licensing and Migration Requirements

Check licensing before creating migration batches.

• Confirm that users have the required Microsoft 365 workload licenses.
• Check Exchange Online licensing for mailbox migrations.
• Verify SharePoint and OneDrive licensing where applicable.
• Confirm Teams licensing for supported Teams migration scenarios.
• Purchase the required Cross-Tenant User Data Migration licenses for eligible cross-tenant migrations.
• Check licensing requirements for Migration Orchestrator if it is being used.

Microsoft states that Cross-Tenant User Data Migration is a per-user, one-time licence and that the required licence can be assigned to either the source or the target user object. Microsoft also states that cross-tenant migrations fail when the required license has not been purchased and assigned appropriately.

This should be checked before migration rather than during the first batch.

5. Prepare Security and Compliance

Review security and compliance settings in both environments in this step of the Microsoft 365 migration checklist.

Check:

• Multifactor authentication.
• Conditional access policies.
• Administrative roles.
• Security groups.
• Data loss prevention policies.
• Retention policies and labels.
• eDiscovery requirements.
• Legal holds.
• Audit requirements.
• Encryption settings.
• Third-party applications and service accounts.

Do not assume that a compliance configuration automatically becomes identical in the target tenant simply because the underlying data was migrated.

For regulated environments, Microsoft recommends involving legal and compliance teams before starting a tenant-to-tenant migration.

6. Check Network and Technical Readiness

At this point of the Microsoft 365 tenant migration checklist, network planning matters, particularly for migrations involving external sources or on-premises environments.

Check:

• Available bandwidth.
• Firewall rules.
• Proxy configuration.
• Microsoft 365 endpoints.
• Source-system performance.
• Migration server capacity, if applicable.
• Service throttling.
• Source-system throttling.
• Microsoft 365 service limits.

7. Plan Exchange, SharePoint, OneDrive, and Teams Migration

This stage of the Microsoft 365 migration checklist states, ‘Treat each workload according to its documented dependencies and limitations.

Microsoft’s current tenant-to-tenant guidance states the following:

• Teams content has dependencies on Exchange mailboxes.
• OneDrive and SharePoint share permission models.
• Migration Orchestrator can handle sequencing for supported workloads.

Different approaches for different workloads are listed below.

Opt for the required migration approach as per your requirement.

8. Run a Pilot Migration

A pilot helps identify problems before the main migration. Now, in this MS 365 migration checklist, you have to select users and workloads that represent the actual environment rather than choosing only simple test accounts.

Test:

• Mailbox migration.
• Email and attachment integrity.
• Calendar items.
• Contacts.
• Folder structures.
• OneDrive permissions.
• SharePoint permissions.
• Teams access.
• Sharing links.
• User sign-in.
• Mail flow.
• Application access

Microsoft recommends starting with a small pilot for SharePoint and OneDrive rollouts and using pilot results to adjust the migration before increasing its scope and speed.

For file-share migrations, Microsoft similarly recommends a small pilot to validate the process, performance, communication, and user feedback before the full cutover.

The pilot should therefore test the process, not just whether data can technically be copied.

9. Execute Migration and Cutover

Once the pilot passes validation, move to production batches.

• Group users into logical migration batches.
• Record the users included in each batch.
• Track migration status and errors.
• Monitor service throttling.
• Maintain migration logs.
• Communicate the cutover window.
• Complete required DNS and mail-routing changes.
• Confirm user access after each migration stage.

10. Validate Migrated Data

Migration completion does not automatically mean the project is complete.

Validate:

• Number of migrated users.
• Mailbox item counts where appropriate.
• Mailbox sizes.
• Email folders.
• Calendar items.
• Contacts.
• Tasks and notes.
• SharePoint files.
• OneDrive files.
• Permissions.
• Sharing links.
• Teams data supported by the selected migration method.
• Mail flow.
• User sign-in.
• Important business applications.

Microsoft’s cross-tenant mailbox documentation specifies the mailbox content that migrates, including email, contacts, calendar, tasks, notes, and specified Recoverable Items folders. It also states that Outbox items do not migrate because they are client-based and stored locally rather than synchronised to the cloud.

This is why validation should cover more than simply checking whether a mailbox exists in the target tenant.

11. Prepare Users and Communication

By this stage of the Microsoft 365 migration checklist, users should know what will change and when.

Communicate:

• Migration date.
• Expected downtime or read-only periods.
• New sign-in requirements.
• Outlook profile changes, if applicable.
• OneDrive synchronisation changes.
• Teams change.
• New URLs or tenant addresses.
• Support contact details.
• Actions users need to take.

Microsoft emphasises user communication as part of migration planning. For example, Microsoft recommends communicating with users before SharePoint and OneDrive moves and explaining when the migration will occur and what users should expect.

Avoid sending a long technical document to every user. Give users the few actions that actually apply to them.

12. Complete Post-Migration Tasks

After migration:

• Review failed and skipped items.
• Validate critical users and workloads.
• Confirm DNS and mail routing.
• Verify permissions.
• Review security policies.
• Confirm retention and compliance requirements.
• Update applications and integrations.
• Remove obsolete migration configurations.
• Remove migration endpoints and organisation relationships when they are no longer required.
• Preserve migration reports and logs.
• Document unresolved issues and their owners.

For cross-tenant Exchange migration, Microsoft specifically documents removing migration endpoints and organisation relationships after the migration is complete.

Do not immediately decommission the source environment simply because the migration batch reports success. Complete the required validation, retention, compliance, and application checks first.

Microsoft 365 Migration Checklist: Final Review

Before closing the migration project, verify these areas:

If you have followed the above Microsoft 365 Tenant to Tenant Migration Checklist carefully and have reviewed the above factors, there are minimal chances of any kind of data loss.

Microsoft 365 Migration Facts and Figures to Remember

Now that you have followed the above O365 migration checklist, a few documented numbers are particularly useful when planning:

• 5 TB / 1 million items: Maximum supported size/item count for an individual SharePoint site in cross-tenant migration.
• 5 TB / 1 million items: Maximum supported size/item count for an individual OneDrive account in cross-tenant migration.
• 400 characters: Microsoft path-length limit relevant to cross-tenant SharePoint and OneDrive migrations.
• 150 mailboxes: Microsoft’s recommended number for a cutover migration, although the documented maximum is 2,000 mailboxes. This applies specifically to Exchange cutover migration, not all Microsoft 365 migrations.
• Up to 100 GB/hour: Throughput Microsoft has observed in real customer deployments for Exchange hybrid migrations. This is an observed result, not a guaranteed rate.

These figures should be used as planning references, not promises. Microsoft explicitly notes that migration velocity varies according to the environment, data, workload, and migration method.

Conclusion

A Microsoft 365 migration checklist should cover more than the transfer itself. Identity preparation, licensing, workload dependencies, supported limits, security settings, pilot testing, user communication, and post-migration validation all affect the result. Microsoft’s current tooling supports both individual workload migrations and coordinated tenant-to-tenant scenarios, so the right approach depends on the workloads and requirements of the project.

The safest approach is to assess the environment first, document the dependencies, test with a representative pilot, migrate in controlled batches, and validate the target environment before closing the project. Where a migration falls outside Microsoft’s native workload coverage or requires additional capabilities, evaluate third-party tools against the specific technical and compliance requirements rather than choosing one based only on migration speed.

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