Office 365 to Office 365 Migration

Updated on Sep 17, 2026 by Deepika Singh

Introduction

Microsoft 365 tenant-to-tenant migration is commonly required when organizations merge, acquire another company, separate business units, consolidate Microsoft 365 environments, or move users from one independently managed Microsoft 365 organization to another.

Moving a mailbox between two Microsoft 365 tenants is different from moving a mailbox between users within the same tenant. The source and destination organizations have separate identities, Exchange Online configurations, domains, permissions, and administrative environments.

• 1. Microsoft's native cross-tenant mailbox migration
• 2. A Professional Regain IMAP Migration tool

Microsoft's native solution provides a supported way to move Exchange Online mailboxes between tenants, but it requires administrator configuration and specific migration prerequisites. Regain IMAP Migration tool provides an alternative workflow for organizations that prefer a dedicated migration interface or need migration capabilities beyond their preferred native workflow.

This guide explains both approaches, the preparation required, what data can be migrated, what happens to the custom domain and Outlook, and what to verify after migration.

What Is Microsoft 365 Tenant-to-Tenant Migration?

A Microsoft 365 tenant-to-tenant migration is the process of moving users, mailbox data, or other Microsoft 365 workloads from one Microsoft 365 tenant to another.

For example:

• Source Tenant: companyA.onmicrosoft.com
• Target Tenant: companyB.onmicrosoft.com

A mailbox migration specifically focuses on moving Exchange Online mailbox data from the source organization to the destination organization.

Microsoft's current cross-tenant mailbox migration supports moving Exchange Online mailboxes between Microsoft 365 tenants. The migration process requires the destination user to be appropriately prepared and mapped to the source mailbox.

A complete Microsoft 365 tenant migration can involve much more than Exchange Online. Organizations may also need to plan migrations for:

• Exchange Online mailboxes
• OneDrive
• SharePoint
• Microsoft Teams
• Microsoft 365 Groups
• Domains and DNS
• Users and identities
• Permissions and sharing
• Applications and integrations

Therefore, migrating a mailbox should not automatically be considered a complete Microsoft 365 tenant migration.

Why Migrate Mailboxes Between Microsoft 365 Tenants?

Organizations may need to move Microsoft 365 mailboxes between tenants for several reasons.

• Company Merger or Acquisition: When two organizations combine, their Microsoft 365 environments may need to be consolidated into a single tenant.
• Business Divestiture: A business unit being separated from a parent organization may need to move its users and mailbox data to a new Microsoft 365 tenant.
• Tenant Consolidation: An organization operating multiple Microsoft 365 tenants may decide to consolidate users into a single environment.
• Organizational Restructuring: Changes to business ownership, subsidiaries, departments, or IT administration can require users to move between Microsoft 365 tenants.
• Changing Microsoft 365 Administration: An organization may also move users to another tenant when Microsoft 365 environments are being reorganized or managed under a different organizational structure.

What Data Can Be Migrated?

Microsoft's native cross-tenant mailbox migration currently supports user-visible mailbox content including:

1. Email messages
2. Contacts
3. Calendar
4. Tasks
5. Notes

Prerequisites for Microsoft 365 Tenant-to-Tenant Migration

Before starting, prepare both Microsoft 365 tenants:

1. Administrator Access: Ensure you have the required permissions in both tenants.
2. Licensing: Verify the required Microsoft 365 migration licenses.
3. Target Users: Create and properly configure users in the destination tenant.
4. User Mapping: Map each source mailbox to its corresponding destination mailbox.
5. Mailbox Holds: Check retention, litigation, or other holds that may affect migration.
6. Domain & DNS: Plan domain verification, MX, Autodiscover, SPF, DKIM, and DMARC changes.
7. Migration Plan: Define migration batches, schedule, verification steps, and contingency procedures.

Method 1: Microsoft 365 Native Cross-Tenant Mailbox Migration

Microsoft provides a native option to move Exchange Online mailboxes between Microsoft 365 tenants. The process requires preparation, user mapping, migration configuration, and validation.

Prepare the Source Tenant

1. Identify mailboxes for migration.
2. Configure the required migration application and Exchange settings.
3. Create the required mail-enabled security group.
4. Verify licenses and mailbox holds.

Prepare the Target Tenant

1. Configure the migration application, endpoint, and organization relationship.
2. Prepare target user accounts and required licenses.
3. Verify tenant settings and connectivity.

Prepare and Map Users

Create the required target MailUser objects and map each source mailbox to its destination.

Example: john@oldcompany.com → john@newcompany.com

Configure and Start Migration

1. Configure the migration endpoint and batch.
2. Run validation checks.
3. Start the migration from the target tenant.
4. Monitor progress and resolve errors.

Verify Migrated Mailboxes

Check emails, folders, attachments, contacts, calendar, tasks, and Outlook connectivity. Also verify internal and external mail flow before completing the migration.

Method 2: Use Regain IMAP Migration tool for Microsoft 365 Mailbox Migration

Organizations that prefer a dedicated migration application can use Regain IMAP Migration Tool to migrate mailboxes directly from one Microsoft 365 tenant to another.

Regain IMAP Migration Software supports direct Microsoft 365-to-Microsoft 365 mailbox migration, so the mailbox data does not have to be manually exported to PST before importing it into the destination tenant.

1. Launch Regain IMAP to IMAP Migration Tool and select the Microsoft 365 migration option.
2. Connect and authenticate the source Microsoft 365 tenant.
3. Load and select the mailboxes and folders you want to migrate.
4. Connect and authenticate the destination Microsoft 365 tenant.
5. Load the destination mailboxes and map source users to their corresponding target users.
6. Review the mailbox, folder, and user selections.
7. Start the migration and monitor its progress.

Regain IMAP to IMAP Migration Tool Features

• Migrate emails directly from one IMAP account to another while maintaining folder structure, email properties, and data integrity.
• Allow to Backup all Microsoft 365 Mailbox to User system in various email formats
• Migrate multiple IMAP mailboxes in a single process with easy source-to-destination mailbox mapping.
• Transfer complete mailboxes or selected folders such as Inbox, Sent, Drafts, Trash, and custom folders.
• Migrate emails along with attachments while preserving the original folder hierarchy.
• Support migration between different IMAP email services, including Office 365 to Office 365, Gmail, Yahoo Mail, AOL, Zoho, Outlook.com, and other IMAP servers.
• Apply selective filters based on folders, date range, and other available criteria to migrate only the required mailbox data.
• Monitor migration progress and generate detailed reports to review successfully migrated and failed items.

Video Tutorial for Regain Office 365 to Office 365 Migration – Watch Now!

Conclusion:

Microsoft 365 tenant-to-tenant migration requires proper tenant preparation, user mapping, licensing, domain planning, and data verification. Regain IMAP Migration Tool provides direct Microsoft 365-to-Microsoft 365 mailbox migration, allowing you to connect both tenants, select mailboxes and folders, map users, migrate data, and verify the results

Frequently Asked Questions

Q 1. Can I migrate a mailbox from one Microsoft 365 tenant to another?

Ans. Yes. Microsoft supports cross-tenant Exchange Online mailbox migration, and third-party tools can also provide tenant-to-tenant mailbox migration workflows. Microsoft's native method requires specific tenant, user, licensing, and migration configuration. You can use Regain IMAP to IMAP Migration tool to complete your task.

Q 2. Can I migrate multiple Microsoft 365 mailboxes at once?

Ans. Yes. Microsoft supports migration batches, while Regain IMAP Migration tool can also support batch mailbox migration depending on the product and license. For large migrations, process users in controlled batches and verify each batch before continuing.

Q 3. What data can be migrated between Microsoft 365 tenants?

Ans. Supported mailbox data can include email, contacts, calendar, tasks, and notes. The exact data transferred depends on the migration method and its supported content.

Q 4. Do I need a special license for Microsoft's native cross-tenant mailbox migration?

Ans. Yes. Microsoft currently requires a Cross-Tenant User Data Migration license for users being migrated. The license can be assigned to the source or target user object.

Q 5. Can I migrate a mailbox that is on Litigation Hold?

Ans. Microsoft's native cross-tenant mailbox migration does not support mailboxes that are on any type of hold. The migration is blocked for those mailboxes.

Q 6. Will the source mailbox remain after migration?

Ans. With Microsoft's native cross-tenant mailbox migration, the source mailbox is deleted after a successful migration and the source user is converted to a MailUser for routing/coexistence purposes.

If using Regain IMAP Migration tool, the source mailbox is not necessarily deleted automatically. Administrators should verify the product's behavior and decide when the source environment can be decommissioned.

Q 7. Do I need to recreate the Outlook profile?

Ans. Not necessarily in every scenario. However, users may need to sign in again or create a new Outlook profile after moving between Microsoft 365 tenants. The exact requirement depends on the migration and identity configuration.

Q 8. Can I migrate Microsoft 365 Groups using native cross-tenant mailbox migration?

Ans. No. Microsoft currently states that Microsoft 365 Groups aren't supported by the native cross-tenant mailbox migration feature.