How to Migrate Mailboxes from One Tenant to Another in Office 365?

Himanshu Goyal    Himanshu Goyal     Updated On - 23 May 2019

Sometimes Office 365 administrators need to migrate mailboxes from one tenant to another, but they don’t find any suitable ways for it. Though there are some manual approaches, they are very complex, and you won’t be able to perform it without proper guidance and technical knowledge. Many queries related to this can be found in Microsoft’s forums too.

So, here we are going to discuss some basics that can help you migrate mailboxes from one Office 365 tenant to another. Also, here we’ll talk about how you can plan the migration.

A Simple Approach to Office 365 Tenant to Tenant Migration

The Office 365 tenant to tenant migration is performed using PowerShell scripts or third-party tools. Before that, there are a few things that you should keep in mind.

Pre-migration Stage

Domain Preparation

Prepare the domain with the following steps:

  • Ensure that you have enough licenses for the target Office 365.
  • Create admin accounts in both the source and target to perform the migration smoothly.
  • Create user mailboxes, room/resource mailboxes, and distribution groups in the target.
  • If needed, perform AD DS consolidation using AD DS tools and sync source domain with the target domain manually or using synchronization.
  • Train your end users regarding the post-migration use of Office 365.
Domain verification
  • Start verification of target tenant domain in Office 365.
  • Add a source domain in the target Office 365 admin center and create TXT records in DNS.
  • Make sure the domain is in use only one tenant. Otherwise, the verification will fail.

  • After performing these steps, it will take around 72 hours for the change to be seen.
Migration Scheduling
  • Generate a list of user mailboxes that are to be migrated and create a CSV file for mapping.
  • Note the lowest value of TTL on MX record (of the primary email domain).
  • Disable directory sync for source tenant (from Office 365 admin center).

Migration Stage

Stop inbound mail flow

Stop inbound mail flow to the source tenant by changing the primary MS record to an unreachable value or by using a third-party service. As you have noted the lowest value of TTL on MX record (of primary email domain) in your preparation step, you can plan the time of this step easily.

Source tenant preparation

Before moving the Office 365 mailbox to another tenant, the primary mail domain should be erased from all objects in the source tenant.

Preparing the target domain

It involves the verification of source tenant in the target domain (do one hour after the previous step).

  • When you use AD FS, you’ll have to configure a new domain in target tenant for AD FS.
  • Activate the new user accounts in the target domain and assign licenses.
  • On the new users, set the source domain as the primary email address (done using Windows PowerShell). Also, decide on communicating the passwords to end users.
  • Now you can route the emails to the new mailboxes.
  • Test the mail flow in and out of the target tenant.

Now it is time to decide on the migration method. You can also decide on the type and amount of data to be migrated. Migration can be accomplished using PowerShell scripts. However, third-party migration tools are recommended as they offer complete control over the migration. They allow to schedule the migration and also to filter the data to be migrated.

Kernel Migrator for Exchange – For a quick and easy tenant to tenant migration

Kernel Exchange Migrator is an advanced tool that is specially designed for Exchange to Exchange migration (same domain, cross-domain, & cross-forest), Exchange to Office 365 migration, Office 365 to Office 365 migration, etc. It allows users to easily migrate every item of their Office 365 mailboxes from one tenant to another. It has some amazing features that make it the best Exchange migration tool for Office 365:

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  • Pre-migration analyzer for advanced planning of migration
  • Allows migration from one Exchange Server to another with any disruption
  • Simplifies migration of data in the cross-forest environment
  • Quick mapping of mailboxes (manually or using a CSV file)
  • Schedules the migration process according to your convenience
  • Keeps track of the migration process with the report console feature

Let’s have a look at the working process of this tool:

  1. Click “Add Project” on the home screen of the tool and provide a name to the project.
  2. Add Project process

  3. Now, create a mailbox migration job by clicking “Add Job” in the toolbar.
  4. create a mailbox migration job

  5. In the mailbox migration job, add the mailboxes that you want to migrate.
  6. add the mailboxes

  7. In the next step, add the target for the mailbox migration and then click “Next.”
  8. add the target for the mailbox migration

    Note: You can apply multiple filters to the mailboxes, such as message classes, date range, and other folder filters.

  9. Now, map the source mailboxes with the target mailboxes. You can map mailboxes automatically or using a CSV file; then click “Next” to continue.
  10. map the source mailboxes

    Note: Kernel Migrator for Exchange allows you synchronize migrated mailboxes; also, you can skip mailboxes if the bad count exceeds the specified limit.

  11. Configure the email notifications, and click “OK.”
  12. Configure the email notification

    Note: You can specify the hours for migration according to your requirements with Kernel Migrator for Exchange. Also, it allows you to schedule the migration based on your preferences. After scheduling the migration job, click “Next.”

    scheduling the migration

  13. Now, specify the time of migration.
  14. specify the time of migration

  15. In the final step, the tool will show you the migration summary before starting the migration. Check the summary and click “Finish.” The migration process will start (as per your specification).
  16. migration process start

  17. Once the migration job is added, it can be managed from the “Projects”:
  18. mange the migration job from project

  19. You can view the migration report by right-clicking on the mailbox migration job. The migration report will be displayed on the screen.
  20.  view the migration report

The migration report can be saved in HTML or PDF format. This way you can quickly perform Office 365 tenant to tenant migration using Kernel Migrator for Exchange tool.


The manual approach to moving mailboxes from one Office 365 tenant to another is very complicated, as it is based on PowerShell scripts. Not every user is capable of using the Shell Scripts because it requires technical expertise. So, Kernel Migrator for Exchange is the best option that allows you to move Office 365 mailboxes from one tenant to another. Even non-technical users can easily migrate their Office 365 data using this tool. Also, you can use this software to migrate your public folders from one Exchange version to another .

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