Office 365 Tenant-to-Tenant Migration Step-by-Step Guide

Moving users from one Microsoft 365 tenant to another requires careful preparation of both the source and target environments. Administrators need to identify the users and data in scope, prepare the target tenant, map source mailboxes to the correct target accounts, migrate the required data, and validate the results before completing the transition.

EdbMails Office 365 tenant to tenant migration supports moving mailboxes and other supported Microsoft 365 workloads between tenants. For migrations involving tenant consolidation, separation, domain changes, or other organizational transitions, review the planning considerations for cross-tenant Office 365 migration before starting the migration.

This step-by-step guide explains how to perform the Office 365 tenant-to-tenant migration using EdbMails, from prerequisites and tenant configuration to mailbox mapping, migration, and post-migration verification.

1. When should you migrate between Microsoft 365 tenants?

   Organizations move users and data between Microsoft 365 tenants for different business and administrative reasons. The migration may involve the entire organization or only a selected group of users.

   Common scenarios include:

   • Mergers and acquisitions: Move users from an acquired organization into the parent company's Microsoft 365 environment.
   • Divestitures: Separate selected users and business data into an independent tenant.
   • Tenant consolidation: Bring users from multiple Microsoft 365 tenants into a central environment.
   • Organizational restructuring: Move departments, subsidiaries, or business units to another tenant.
   • Rebranding and domain changes: Move users to a new tenant as part of a company or domain transition.
   • Business separation: Split users and data when business units need to operate independently.

   The migration approach depends on the number of users, mailbox sizes, target configuration, domains, workloads, and planned cutover. Identifying these requirements early helps determine how users should be grouped and how the migration should be carried out.

2. What to plan before a Microsoft 365 tenant migration

   Start by defining what needs to move and how the target environment should look after migration. Create an inventory of the users, mailboxes, domains, and workloads included in the project.

   For each user, record the source mailbox, intended target mailbox, mailbox type, approximate size, licensing status, and migration batch. This is particularly useful when source and target addresses differ, or users are being moved in phases.

   Define the migration scope

   Identify the mailbox data that needs to be migrated. Depending on your environment, the scope may include:

   • Primary user mailboxes
   • Shared mailboxes
   • Archive mailboxes
   • Public Folders
   • Email folders and supported mailbox items
   • Mailbox permissions that need to be verified or reconfigured

   Prepare the target tenant

   Set up the target Microsoft 365 tenant before beginning production migration. Microsoft's Tenant roadmap for Microsoft 365 guides preparing tenant configuration, identities, domains, services, and licensing.

   Confirm that the required target users, mailboxes, licenses, accepted domains, administrative access, and target email addresses are ready.

   If source and target addresses differ, prepare the mappings before migration.

   If the same custom domain needs to move from the source tenant to the target, plan the domain transition separately. The Office 365 migration with the same domain guide explains the considerations for this type of move.

   Check network readiness

   Migration performance can be affected by mailbox volume, workload type, batch size, available bandwidth, and Microsoft 365 service conditions.

   Before starting a large migration, verify that the migration computer and network connection have sufficient and stable bandwidth. Microsoft's network and migration planning for Microsoft 365 guidance can help you evaluate bandwidth and connectivity before production migration.

   Use the pilot migration to observe actual migration behavior in your environment before deciding how many users to include in each production batch.

   Plan migration batches

   For larger environments, divide users into manageable batches instead of migrating every mailbox at once.

   Users can be grouped by department, location, mailbox size, business priority, or planned transition date. Working in batches makes it easier to monitor progress, validate results, and resolve issues before moving the remaining users.

   Run a pilot migration

   Before starting the full production migration, select a small group of representative users for a pilot.

   Where possible, include users with different mailbox sizes and mailbox types. Use the pilot to confirm authentication, mailbox loading, source-to-target mapping, migration settings, target accessibility, reporting, and the validation process.

   Once the pilot results are verified, use the tested process for the remaining migration batches.

3. Office 365 tenant-to-tenant migration prerequisites

   • EdbMails product prerequisites — source Office 365 tenant

     1. You'll need a global admin account for automatic registration of the EdbMails application on your Entra ID (Azure Active Directory). If you prefer, a global admin account or any user account with full access rights works equally well for manual registration.

   • Microsoft 365 / scenario prerequisites — target Office 365 tenant

     1. Set up your target Office 365 tenant using the Tenant roadmap for Microsoft 365 as your reference.
     2. Review the available licensing plans and pick one that fits your organization's needs. A 30-day free trial lets you validate your requirements before selecting a plan. The Office 365 business plans comparison and enterprise plans comparison are good starting points.
     3. Mailboxes need to be prepared on the target tenant before migration. If you plan to use EdbMails automatic mailbox creation or license-assignment functionality, verify the current product prerequisites before production. If you prepare target users and licenses manually, these resources cover the Microsoft 365 process:
        • Add users and assign licenses to Office 365 users
        • Add several users at the same time to Office 365
        • Assign Microsoft 365 licenses to user accounts
     4. If public folders are part of the migration scope, make sure they're created on the target tenant and that admin permissions are correctly assigned. See create and assign public folder permissions in Office 365.
     5. For In-Place archive migration between tenants, the archive mailbox must be enabled on both the source and the target. Follow the steps to enable online archive in Office 365.

          See the full guide to migrate archive mailboxes to Office 365.

     6. Assign the Organization Management role group in Exchange Online to the admin user. This elevated permission is required specifically for public folder migration.
     7. If you plan to keep receiving emails on a custom domain from the source tenant, that domain needs to be added and verified on the target Office 365 tenant.

         You'll need a global admin account with an active mailbox for automatic registration of the EdbMails application on your Entra ID (Azure Active Directory). If you prefer, a global admin account or any user account with full access rights works equally well for manual registration.

     8. For environments running Active Directory Federation Services, review the target-domain configuration required for your environment.
     9. If your project includes messages near Microsoft 365 service limits, verify the current supported message-size settings before migration. See the EdbMails message-size guidance and current Microsoft 365 limits before changing tenant settings.

4. Office 365 Tenant to Tenant migration steps using EdbMails

   • Step 1: Download and install EdbMails software

     • Download and install EdbMails on your computer. It’s compatible with all Windows server and client operating systems.
     • Open the EdbMails application, enter the email and password you used to sign up on the EdbMails website and click ‘Login.’ Alternatively, you can click ‘Start Your Free Trial.’
     • Check the detailed system requirements for EdbMails Office 365 Tenant to Tenant Migration.

       

     • Choose the ‘Office 365 Migration’ option

       

     • Select ‘Office 365 to Office 365 migration’

       

     • You can either keep the default job name or click the 'New Job' button to specify job name of your choice.

       

   • Step 2: Connect to source Office 365 Tenant

     • Click on ‘Add New Connection’ to add a new connection to the source Office 365. In case you already have a connection, select it from the list and click on ‘Connect to Existing’ to proceed further.

       

     • Select the required connection options and click on ‘Next’ to continue.

       

     • Choose the proper source authentication method and click on ‘Login’ to proceed.

       

         Connect to the Office 365 server using secure modern authentication.

        Log in on the Microsoft sign-in page using a global admin account that has an active mailbox.

       

     • After successful authentication, choose a method to load the mailboxes. EdbMails automatically retrieves mailboxes from your source Office 365 server. If the required mailboxes aren’t visible through this method, you can also upload them using a CSV file. Alternatively, you can load mailboxes from a previously saved list for convenience.

       

   • Step 3: Select the mailboxes from the source Office 365 Tenant

     • Select the mailboxes and folders from the left pane of the main migration window to proceed.
     • Click ‘Next’ to set up the connection with the target Tenant.

       

        Tip: If this is your first migration using EdbMails, it will be a full migration. For any subsequent migrations from the same source to the target, the process will be incremental.

   • Step 4: Connect to target Office 365 tenant

     • Click ‘Add New Connection’ to establish a new connection to the target Office 365. If you prefer to use an existing connection, select it from the list and click ‘Connect to Existing’ to proceed.
     • Select the appropriate connection options and click ‘Next’ to continue.

       

     • Select the appropriate target tenant authentication method, click ‘Login’ to proceed, and authenticate via the Microsoft sign-in page.

       

     • Choose a method to load the mailboxes. Alternatively, you can upload the mailboxes using a CSV file.

       

   • Step 5: Map source and target tenant mailboxes

     • Select the appropriate option to map the mailboxes between the source and target tenants.

       

     • You can choose to let EdbMails automatically create and license target Microsoft 365 mailboxes, or use existing target mailboxes based on your migration requirements. Review the automatic mailbox creation and licensing requirements before using this option.
     • For source-to-target mapping, EdbMails supports automatic mapping, manual mapping, and CSV-based mapping. Use manual or CSV mapping when you need customized source-to-target mailbox or folder mapping. See the user-defined mailbox and folder mapping guide for details.

   • Step 6: Start Office 365 Tenant to Tenant migration

     • Once you have completed the mailbox mapping, Click the ‘Start Migration’ button to begin the migration process.

       

     • The migration process has begun. Once completed, a notification will appear. You can click the ‘View Log’ button to review the migration report.

       

5. Best practices for Microsoft 365 tenant-to-tenant migration

   A few practical checks can make a large migration easier to manage and validate:

   • Inventory users, mailboxes, domains, and workloads before migration.
   • Confirm target users and licensing early.
   • Verify network readiness before production migration.
   • Test the migration with a representative pilot group.
   • Divide larger environments into manageable batches.
   • Identify large or complex mailboxes during planning.
   • Verify source-to-target mappings before starting each batch.
   • Apply migration filters only where the project requires selective migration.
   • Review migration reports after each run.
   • Validate representative mailbox data directly on the target.
   • Keep source-to-target mappings consistent for repeat migrations.
   • Coordinate domain and DNS changes with the planned cutover.
   • Keep the source tenant available until the migration has been validated.
   • Record and resolve migration exceptions before closing the project.

6. Microsoft 365 tenant-to-tenant post-migration checklist

   • Step 1: Resolve failed or skipped items and rerun if required

     Review the EdbMails migration report and resolve any prerequisite, access, mapping, failed-item, or skipped-item issues before final cutover. Run the supported repeat/incremental migration when additional mailbox changes need to be transferred.

   • Step 2: Complete the mail-flow or domain cutover for your scenario

     Update MX, Autodiscover, DNS, or custom-domain settings only when they are required by your migration scenario. If the same custom domain is moving between tenants, follow the dedicated Office 365 migration with the same domain procedure rather than treating domain transfer as a generic migration step.

   • Step 3: Confirm Outlook and user readiness

     • Confirm users can sign in to the target environment and access the expected migrated mailbox data.
     • If Outlook will not connect to the target mailbox, review the steps to recreate the Outlook profile after migration.
     • If needed, review Outlook Auto-Complete suggestions after the tenant change.
     • After mail-flow cutover, send and receive test messages for representative users before sign-off.

   • Step 4: Decommission source licenses or domains only after approval

     Remove source subscriptions, licenses, or domains only after migration validation, mail-flow checks, user readiness, and business approval are complete. See Microsoft guidance before cancelling a Microsoft 365 subscription.

7. When does a tenant migration tool make sense?

   The migration approach depends on the size and complexity of the environment, the number of users, administrator experience, available migration window, and the workloads that need to move.

   For smaller projects, administrators may first evaluate the available Microsoft migration options and determine whether they meet the project's requirements.

   When a migration involves multiple mailboxes, different source and target addresses, migration batches, selective data migration, mailbox mapping, repeat migrations, and reporting, using a dedicated migration application can make these activities easier to manage from one workflow.

   EdbMails Office 365 tenant to tenant migration provides the migration workflow for supported mailbox data and related Microsoft 365 workloads. The product page provides details about supported migration scenarios, features, licensing, and the free trial.

---

Additional resources:

• EdbMails Office 365 migration software
• Office 365 migration guide
• Cross-tenant Office 365 migration
• Office 365 public folder migration
• Office 365 public folder to shared mailbox migration
• Office 365 archive mailbox migration