5 Tips for Migrating Mailboxes between One Microsoft 365 Tenant to Another

5 Steps for Migrating Mailboxes between Microsoft 365 Tenants

By Sridhar Chalapathy  |  Published on August 9, 2022

5 Steps for Migrating Mailboxes between Microsoft 365 Tenants


There are numerous reasons why organizations will want to migrate from one tenant to another or consolidate different tenants. Some instances when an organization considers tenant-to-tenant migration are mergers, acquisitions, divestiture, or rebranding, which requires migration of mailboxes, instances, domains, and OneDrive accounts from one tenant to another.  

An organization might sometimes end up with multiple Microsoft 365 tenants across different components, or sometimes businesses are consolidated in case of mergers or acquisitions. In some instances, to meet the growing needs of the organization, information in Microsoft 365 may have to be restructured. For instance, the Teams structure may have gotten too complex or there may be too much sprawl, etc. Whatever the reasons are, organizations need to consider many crucial factors before they initiate a Microsoft 365 tenant to tenant migration.  

A tenant comprises of the users in your organization as well as all the vital data about them- their passwords, profile data, and permissions, apart from the information about the company such as applications, groups, even security, and much more. In short, in Microsoft 365, the tenant represents your organization. 

Things to Consider During Cross-tenant Mailbox Migration

5 Steps for Migrating Mailboxes between Microsoft 365 Tenants

In some scenarios such as business mergers, the mailboxes must be migrated to another tenant. Mailbox migration can be a non-linear process requiring thorough planning and groundwork, meeting specific preconditions, and procuring licenses. In this blog post, we will look at some of the steps you need to undertake to migrate the mailbox from one Microsoft 365 tenant to another. 

Plan the process in advance 

It is vital to plan the process well ahead (minimum 15 days before the project due date) to ensure a smooth migration, without hurdles or setbacks. Every prerequisite of the migration such as acquiring the required licenses must be considered. Before moving any data, it is important to understand exactly what resides in the current state source environment. You need to have a complete and detailed picture of the following while planning a successful tenant migration:  

  • All users along with their settings/rights 
  • Mailbox specifications for every user 
  • Groups that are established and the users who are in each group 
  • Every application that is being used, which users/groups are using each application, and which applications are due for updates 
  • Data entities and where they are stored, their size and how frequently they are accessed, what they are used for and by which applications 
  • How and where the data entities are backed up 
Prepare the tenants

The target and source tenants must be prepared for the migration of mailboxes. A few examples of such preparation- admin accounts will be needed for both target and source tenants. Sometimes, prior to the migration, objects such as Users, Groups Resources, and Rooms will have to be created from the target tenant’s source tenant. In some instances, an extra room would have to be created for new users’ mailboxes in the target tenant. 

When possible, go for a Big Bang migration 

The Big Bang migration is usually performed for projects of a smaller scale. In this approach, a major part of the migration implementation and cutover happens during a weekend or overnight. Big Bang migration is the preferred method for small data instances and the most efficient as well as structured migration approach. With the help of innovations and advanced technologies, it has become common to see larger migrations getting concluded over a weekend. 

Monitor any security controls you relax

It is necessary to review the security settings and permissions to understand the differences between the source and target tenants. Before initiating a tenant migration, it is necessary to understand your own security posture. Questions such as ‘Are you migrating from a low-security tenant to a high-security tenant or vice-versa?’, ‘Are there differences in MFA (Multi-Factor Authentication), mailbox auditing, or login auditing’? There will be profound consequences if you are compromised in any way before the migration begins. Make sure to constantly monitor any security controls you relax to ensure the migration process is secure and have a plan in place for security within the new tenant. Once considered an additional precaution, MFA is now a baseline security necessity. It is simple and one of the most effective security practices to prevent unauthorized access. 

Steps to follow on the D-day 
  • Prevent the source tenant from receiving emails 
  • Make sure to configure the source target domain that is to be migrated to the target tenant 
  • Confirm the target domain with the source tenant domain 

Microsoft cloud services are crucial to your business, but Microsoft cloud services and technologies can be a drain on your organization’s IT resources. It is important that you choose the right migration partner and a migration process that is best suited to your organization. As a Microsoft Gold Partner, armed with domain expertise and vast experience in Microsoft technologies, Netwoven is best suited to offer tailor-made solutions that are perfectly suited for your business needs and help you leverage the full potential of the Microsoft cloud. 

We hope you found this blog useful in learning about the various steps to follow while migrating mailboxes from one Microsoft 365 tenant to another. Please reach out to us so that we can put our decades of experience and expertise in migration services and Microsoft technologies to help you in your organization’s Digital Transformation journey.  

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