Home » Blog » Office 365 » Migrate from One Office 365 Tenant to Another with Mailbox Email Data Precisely
Office 365

Migrate from One Office 365 Tenant to Another with Mailbox Email Data Precisely

Published By Mohit Jha
Nimisha Ramesh
Approved By Nimisha Ramesh
Published On January 17th, 2024
Reading Time 12 Minutes Reading

Organizations that utilize Microsoft’s services often need to migrate from one Office 365 tenant to another in their lifespan. This data shifting is becoming more complicated day by day with an increase in volume scope and intermingling of services. 

Apart from the natural complexity of the operation, there are also many points of failure. IT admins have the responsibility to carry out the correct association of thousands of mailboxes each with hundreds of individual emails. If proper precautions are not taken into account they can cause delays in the migration. 

That is why we have come up with this guide. It contains all the important points to be covered while planning, executing, and completing a multi-user email transfer. Moreover, if you have any confusion about whether or not migration is necessary then don’t worry.

We have outlined some scenarios that need mass email transfers between O365 tenants. Go through them and match your particular case.

Why Migrate Mailbox from One Tenant to Another at All?

  • Acquisitions and Mergers: This is the case when an organization takes over another or two rival businesses join to make a new entity. Both of these scenarios need a follow-up with user mailboxes arriving in a single tenant
  • Divestitures: Opposite of merger. They can be a soft divestiture in which only the departments are divided. Companies do it to better optimize their workforce. Like for example marketing team is split into online and offline teams. Another form of divesture is Hard divesture. It is when the host company breaks up either voluntarily or due to regulatory obligations. Both of these require that the employee mailbox shifts into their new tenants.
  • Revamping Brang Identity: This is when an organization changes its name to shift its priority or better identify with its product set. A name change is just part of the revamping. As it includes behind-the-scenes tasks like tenant updation with user data.
  • Update Digital Infrastructure: Infrastructure even if it’s digital can degrade over time. Users not following policies, data storage protocols being violated, etc. So, instead of spending resources on cleaning up an old tenant. This comes at a risk of losing and risking data loss. Instead, many companies may use it as an opportunity to migrate from one Office 365 tenant to another that is completely new. 

Now that the reasons are clear don’t just jump into the migration headfirst. Use the list of the best practices and use to plan out your migration.

Best Practices to Migrate Email from One Office 365 Tenant to Another

Emails are the backbone of both inter and intra-business levels. Moreover, losing access to historical email data post-migration is not a scene that any admin wishes to witness. Therefore, to make sure you have answers to all the questions that are given below:

What is the organization’s expectation out of this migration? 

Knowing about your organization‘s expectations helps in forming a custom plan aligned to achieve all requirements. These include but are not limited to the Timeline of the project. Enhancements in user productivity. More secure environment, etc.

Once the objectives are set ask yourself how can I make migration secure?

The main problem is that the normal security protocols like firewalls,/antivirus are shut down temporarily. This allows attacks to slip in and damage vulnerable data. So to combat it IT admins need to use clever tactics. 

One way to improve security is keeping the migration project a secret and only sharing it on a need-to-know basis. Moreover, the migration environment should be disconnected from all unsecured external networks. If possible use physical barriers like airgaps.

Why should I spend time making a backup if I am about to migrate a mailbox from one tenant to another? 

Even with all preparations migration can be unpredictable. So to protect against this unpredictability admins must make a backup. This backup should include all the items that qualify for migration. Moreover, if the target tenant is not new then build a backup of the target data too. This is to form a safety net against unwanted data overwriting issues. 

Migration is taking more resources than expected what to do?

If resource availability is an issue then schedule the migration during off hours. Use weekends and holidays to conduct most of the migration. Remember, speed should never supersede security in a migration. Now Let’s start with the premigration phase.

Before You Migrate from One Office 365 Tenant to Another Do this

Make Tenant Migration Ready

Tenants by default cannot be considered migration-ready. As they are programmed to handle mailbox data. So to align them for the migration admins need to perform a list of changes. 

In the source tenant, limit new user data creation by setting forwarding rules, daily data caps, etc. This reduces the overall strain of the migration. 

Likewise inside the target tenant set up new user licences. This is to accommodate all new members who are about to join the target tenant. All of this is to be done manually. However, there are tools like Active Directory Domain service which can assist in these tasks. 

Verify Tenant One-by-One

Tenants use domains to talk with each other. If those domains are not verified then no communication can take place. Which in turn stops any attempt to migrate from one Office 365 tenant to another. 

Before starting the migration open the destination Microsoft 365 admin center. Go to the DNS settings and add the TXT record for the SOurce tenant domain.

If you have a custom domain then contact your Domain Registrar to add the DNS settings. Changes can take anywhere from half an hour to three days to complete.

End Directory Sync for the Source Tenant

A directory that is linked to its AD cannot be shifted from one tenant to the other. So admins must first put an end to this operation. As it takes a full day for the request completion this should be done in advance to avoid last-minute migration delays. User and Group level provisioning also needs the same treatment following the delinking.

Tenant Migration Cannot be scheduled Without a Current User List. So create a CSV file with a user mailbox list

Collecting the data is not enough. We know not all data is of the same quality. Moreover, old systems are notorious for having inflated mailboxes. Spending all this effort only to have the same problems resurface at the destination is not in anyone’s best interest. That’s why admins need to perform a data cleanup of the collected items. To speed up the cleanup put users in charge of their data. An added advantage of this distributed cleanup is eliminating the threat of accidental deletion.

On the Day You Migrate from One Office 365 Tenant to Another

Prepare the Source tenant

  • Remove all source tenant objects before migration. 
  • Remove Lync licenses from source tenant users
  • Reset email addresses in DL, and rooms back to the source tenant domain.
  • Delete all secondary emails still in use

Prepare the Target Tenant

  • Verify the source domain in the target tenant then remove it from the source (Keep at least one hour difference between the two).
  • An optional task is to configure auto-discover CNAME for internal/external use. If your organization uses ADFS then also configure the new domain here.
  • For all new users maintain the source domain as the primary one
  • Complete password configuration (If Not Using Sync Features).
  • Reroute all mails by directly updating the MX records of the source tenant. Moreover, verify mail flow to/from new mailboxes.

Professionally Migrate from One Office 365 Tenant to Another

Those who are part of a tent migration for the first time need to know one thing first. Microsoft has no provision, tool, or method to complete this task as of yet. Moreover, it recommends the use of external tools as the only available method to complete Mailbox transfer. 

In the market of such utilities, one tool that stands apart from the rest is the Office 365 to Office 365 Migration Software. Be it price, security or speed the tool outperforms the rest. Becoming the best way to shift mailbox data from one tenant to another in the M365 environment.

Download Now Purchase Now

Working Steps for the Tool to Migrate Mailbox from One Tenant to Another

Step 1. Download, Open, and Use the options within the setup tab to pick Office 365 as both the source as well as the destination platform.

Start screen

Step 2. Make workload selections with the help of checkboxes. After which you can set the start and end date from where to pull data from.


Step 3. In the source tab put the Admin Email and the Application ID you generated beforehand. Validate then push the Next button.


Step 4. Similarly, enter the target information Validate like before, and Press Next.


Step 5. The user’s tab of the tool allows you to have 3 different mapping options to migrate from one Office 365 tenant to another. Choose the one that suits you the best.


Step 6. On the Migration tab, you get the entire user list inside the dashboard. Now make your selections, apply priority if need be, and Validate the result.


Step 7. Finally, hit the Start Migration button to begin the transport of mailboxes from one tenant to the other.


Also Read: How to Transfer Office 365 Subscription to Another Account?

Other Major Considerations While Migrate Email from One Office 365 Tenant to Another

Carry out a pilot Migration to test out all settings

A pilot migration is a miniature version of the actual migration complete with all different data types in a smaller volume. Once the pilot test is successful carry out the rest of the migration. Use the same steps as in the trial run. 

Choose a Migration Methodology 

Broadly speaking there are two ways to approach migration. 

Either move all users at once. This is called a big-bang migration. It is preferred when the number of users doesn’t exceed 500. Another option is to split the users into different batches. After admins treat each batch as a single migration scenario. This sort of approach is common in migrations where the number of users is more than 500. Both these approaches are supported by the tool admins and are free to add users batch-wise or all at once.

Post-Migration Protocol to Follow After Moving Mailboxes

The first and foremost of the post-migration tasks is to carry out alpha testing of the new environment. Meaning asking users to verify credentials, send out dummy emails, and check historical data. 

If items are missing then use the retry failed items feature of the tool to bring them in. Cross-verify the actual data with the auto-generated report that you get from the tool. In case of a major chunk of missing data, the tool has provisions to migrate from one Office 365 tenant to another again. No configuration steps are required just use the Re-run migration feature and let the tool handle the rest.

In a professional setting mails never stop coming. It is even true during migration as the mailing facility is only paused for in-house users, not external agencies. So as a result there is a guaranteed backlog of newly arrived dta that is yet to be migrated. In other cases, Admins have to either restart migration leave the newly arrived data, or make an embarrassing request to resend all emails. 

Instead of doing this those who have the tool can apply the delta migration feature. It is designed to pick only newly arrived items in the tenant. Recheck all items if the result matches expectations then migration is complete. You are free to terminate the source side tenant as part of the clean-up operation.

Challenges of Migrating Mailbox from One Tenant to Another and How to Overcome Them

  • Maintaining coexistence with the source server. Although the majority of the users don’t need it. In certain industries, security policy might forbid the admin to decommission the old tenant. Even Microsoft itself has no guidelines for such a case. So we suggest that you use the various filtering capabilities of the tool to only migrate a small subset of data. After which you can keep the rest of the source server as it is.
  • Negative return on investment is another issue that many users complain about. Believe it or not, migration is a form of investment. Companies should only carry it out if they feel it will make their workplace more productive. In other words, bring in more money than they spend. If this is not the case then even after successful data transfer migration is considered to be a failure.
  • Visible costs like the price of the tool are highly scrutinized and rightly so. However, admins should also make note of hidden costs like downtime suffered due to migration. 
  • User training. Ideally, this should begin before the migration itself. However, due to workplace commitments, this might not always be possible. Moreover bringing all the different kinds of individuals to equal training levels is easier said than done. So IT admins should maintain communication with HR and set up a training program. Without it, the migration gains cannot be realized.

Related: Forward Email to Multiple Users in Office 365


Inside this guide on how to migrate from one Office 365 tenant to another users got exactly what they were asking for. Complete with best practices, and all steps to perform before during, and after migration.

Moreover, with this tutorial, you can plan and remedy any potential issues ahead of time.  Apart from this, the absence of a manual method makes the tool irreplaceable in any migration scenario. So use it and complete your migration quickly and securely.



Happy Clients






Years of Experience