Office 365 Cross-Tenant Migration: Safely
Transfer Emails, Files, And Settings


Organizations frequently need to migrate data between Microsoft 365 tenants during events like mergers, acquisitions, divestitures, or rebranding. This process, known as Office 365 cross-tenant migration, involves transferring emails, files, user accounts, SharePoint sites, Microsoft Teams data, and security settings while maintaining data integrity and minimizing disruptions.

Cross-tenant migrations necessitate careful planning in areas such as domain management and compliance, as inadequate strategies can result in data loss, operational downtime, and access issues that jeopardize business continuity.

This guide provides best practices for securely transferring emails, files, and settings during an Office 365 cross-tenant migration to facilitate a seamless transition. 


Understanding Office 365 Cross-Tenant Migration


Cross-tenant migration in Office 365 involves transferring data, users, and configurations from one Microsoft 365 environment to another. This process can be complex due to various factors.

  • Microsoft lacks built-in capabilities for comprehensive tenant-to-tenant migrations, necessitating the use of external tools to achieve a complete transition.

  • Additionally, any custom domains will need to be detached and reverified, which may lead to interruptions in email services.

  • It is essential to maintain data integrity, permissions, and security protocols throughout the various Microsoft services involved.

Common reasons for cross-tenant migrations include:

  • Mergers & Acquisitions (M&A): Integrating various IT systems into a unified Microsoft 365 platform.

  • Divestitures: Dividing a business unit to establish it as an independent entity.

  • Rebranding & Domain Changes: Transferring data to a new tenant associated with a different corporate identity.

  • Regulatory Compliance: Complying with industry regulations necessitating a change in tenancy. Visit this link to learn more.


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Best Practices for a Secure and Efficient Cross-Tenant Migration


1. Conduct a Pre-Migration Assessment

Before starting the migration, perform a comprehensive audit of your current tenant to identify:

  • Mailboxes that are either active or inactive, along with OneDrive accounts and SharePoint sites.

  • Dependencies related to Microsoft Teams, encompassing chat logs and file storage solutions.

  • Custom domain names and DNS records that will necessitate reconfiguration.

Leverage reports from the Microsoft 365 Admin Center, PowerShell scripts, or third-party assessment tools to collect this information. This evaluation aids in proactive planning for data volume management, user distribution, and essential security adjustments.


2. Choose the Right Migration Strategy

Selecting the correct migration approach depends on business needs, downtime tolerance, and data complexity.

  • Cutover Migration: Transfers all information simultaneously, making it particularly suitable for smaller organizations with a limited number of users.

  • Staged Migration: Facilitates data migration in stages, minimizing risks and downtime for large enterprises.

  • Hybrid Migration: Ensures that both tenants remain operational throughout the migration process, prioritizing minimal disruption.

3. Manage Custom Domains and DNS Configuration

To transfer a custom domain to a new tenant, it must first be removed from the current tenant. This process can take up to 72 hours and requires careful planning to avoid email service disruptions.

  • To accelerate the propagation, lower the TTL settings on DNS records before migration.

  • Have a plan for updating MX records and verifying SPF, DKIM, and DMARC in the new environment.

  • Consider email forwarding or dual delivery to prevent potential email loss during the transition.

4. Use Secure Migration Tools to Prevent Data Loss

Manual migrations using PST exports and imports increase the risk of data corruption, file loss, and permission issues. To reduce these risks, it is recommended to use secure, automated migration solutions with features like logging, encryption, and validation.

Recommended tools include:

  • Microsoft provides the Cross-Tenant Mailbox Migration Tool for Exchange Online.

  • For OneDrive and SharePoint data transfers, users can utilize the SharePoint Migration Tool (SPMT).

  • For larger migration efforts, tools like BitTitan MigrationWiz, Quest On Demand Migration, and AvePoint are also available.


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5. Migrating Emails, Files, and Settings

The migration process varies depending on the workloads being transferred.

Email Migration (Exchange Online Mailboxes)

  • Utilize Microsoft’s Cross-Tenant Mailbox Migration or alternative third-party solutions.

  • Set up mail forwarding to avoid any email delivery complications during the migration process.

  • After completing the migration, confirm that MX records and autodiscover configurations are properly updated.

OneDrive and SharePoint Migration

  • Utilize Microsoft’s SharePoint Migration Tool (SPMT) or consider alternative third-party options for your migration needs.

  • Transfer files, along with their associated permissions, sharing configurations, and metadata.

  • It is essential to verify that OneDrive links and shared folders continue to be accessible following the migration process.

Microsoft Teams Migration

  • Utilize the Teams migration tools to move chats, channels, files, and tabs to the new environment.

  • Revise Teams policies, adjust guest access configurations, and modify permissions within the new tenant.

  • Re-establish integrated applications and bots in the destination tenant.