Cross-tenant Microsoft 365 migration: Pro tips for a smooth process

There’s a lot to think about before you begin a Microsoft 365 tenant-to-tenant migration. These tips will help you ensure the process is smooth and efficient. 

Cross-tenant migrations can be a headache, but they don’t have to be! Whether onboarding to Microsoft cloud or moving within tenants, mastering best practices can make it smoother.

In this article, we’ll guide you through key steps, from prepping your source tenant to handling complex issues like identity access management (IAM) and mailbox migrations—all while ensuring security and compliance are top priorities.

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What is a Microsoft 365 cross-tenant migration?  

A Microsoft cross-tenant migration typically occurs when your business is going through a merger or acquisition. In these circumstances, combining multiple Microsoft 365 tenancies into one tenant centralizes IT management making it much easier and more secure.

Migrations also enhance collaboration across multiple teams by bringing them all together into one tenant. 

There are a few common scenarios where cross-tenant data migration makes sense if: 

• Your organization has been acquired by another or divided into two or more separate entities 
• Your organization is composed of scattered businesses with separate tenants 
• One or more areas of your organization introduced a new tenant without consulting the IT team 

The goal of a tenant-to-tenant migration is to move content, such as SharePoint sites, Teams channels, shared drives, and Planner plans, from one tenant to another (ideally, with as few surprises as possible). 

Depending on what you need to move, your cross-tenant migration for Microsoft 365 might include a SharePoint migration, a OneDrive migration, a Teams migration, or a group migration. 

Every successful migration starts with a plan  

The objective of a tenant-to-tenant migration is to move content from one Microsoft 365 tenant to another destination environment. With such a major transition, there are a lot of critical questions that you’ll need to consider as you plan your data migration strategy.   

• What are you migrating? Do you need to do a cross-tenant migration of Microsoft 365 in its entirety? Or do you just need to do a cross-tenant OneDrive migration or a cross-tenant SharePoint migration?  
• Are you migrating user accounts, email inboxes, Teams content, or all three?  
• Do you have optimal visibility into all the environments that contain the relevant data and information? 
• What workloads are being used in the source tenant that are different from the target? 
• Have you prepared the source and destination tenants for the migration? Do you have stale content, orphaned users, or checked-out documents at the source? 
• Do you have a plan in place for identity and access management? 

• Have you done any contingency planning to guide you if you encounter problems during the migration?  
• Have you thought about all the relevant legal and regulatory considerations?  

Addressing all these questions before you begin your migration will be critical to achieving a successful migration.   

Plan for identity and access management (IAM) from the start

Handling the identity components of a Microsoft 365 tenant-to-tenant migration is arguably one of the trickiest aspects you’ll encounter. Every project is different, and there are several courses of action to choose from. 

Some of the things people place in the identity category include user and service accounts, Microsoft Entra ID guest users, application registrations, domains, third-party identity management solutions, contacts, and distribution lists. 

So what does IAM look like?

In a nutshell: You need to centralize IAM by establishing directory synchronization between the source and destination tenant and declaring the source Microsoft Entra ID as authoritative (for moving items). 

Let’s say, for example, that your organization has 25,000 users and you acquire a business with 500 users; the new business must abide by the new parent company’s rules. In these situations, most enterprises will provision and migrate new accounts to the destination. 

Bringing the users under their own security management is one way to overcome problems when the acquiring firm does not wish to bring the source environment up to par with their standards. Frankly, this is a faster and simpler solution. 

Planning for IAM might help to assess whether you are ready for migration. Still unsure if you’re ready? Ask yourself the following questions: 

• How will directory objects for both the source and the target tenants be acquired and kept up-to-date throughout the migration project?
• Does a trustworthy directory exist?
• Will account disablement, attribute modifications, and removals be kept across directories?
• Has the target tenant generated the relevant accounts and groups that are currently present in the source tenant?
• Are there certain matching property values that can be used to link objects together?

You might discover that your business isn’t quite ready to start migrations based on the responses to these questions. It’s crucial to think through how to control identities access throughout the migration process. 

Playbook

Tenant-to-tenant migrations

How to efficiently plan and execute migrations for mergers & acquisitions or a reorganization.

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Preparing your source tenant for migration

The first step, like with any migration, is to make the necessary preparations in your source tenant. There are two high-level steps to keep in mind during the preparation stage: 

1. Analyze and define
2. Plan

1. Analyze and define

Don’t fall into the trap of thinking that migration is simply a matter of copying data from one place to another. A successful migration requires a deep understanding of your current environment and a clear vision for your future state. 

You will need to identify applicable quantity structures, pre-existing configuration parameters, and the data volumes to be transferred—but in order to do so, IT professionals must first conduct an analysis of the source environment. 

Some big questions may be answered at this stage. For example, are we making the necessary modifications in the target environment? This can only be identified by investigating the initial situation in the source tenants. ShareGate can help with this. 

There are loads of features in the “Plan” section of the ShareGate app that will give you all the visibility you need.  

For example, our source analysis report will give you insight on exactly what you have and where it’s located, helping you:

• Understand the scope and state of your content: Get a clear picture of what you’re dealing with, from the volume of data to the complexity of your site structures. 

• Create an inventory: Identify all your data, access permissions, workflows, and potential issues hindering the migration process. 

• Pinpoint problematic areas: Discover large sites, teams, or other content that may need to be split or reorganized to ensure a smooth transition. 

By gaining this comprehensive understanding, you can develop a tailored migration strategy that goes beyond a simple lift-and-shift approach. You’ll be able to identify potential roadblocks, optimize your migration process, and ensure a successful transition to your new environment. 

That’s only the beginning! ShareGate offers a wide range of targeted reports to ensure you don’t jump blindly into your tenant-to-tenant Microsoft 365 migration.  

Then, you formulate a vision of the architecture from the current state to the target state for the migration. If you want to identify the target state and the procedures to get there (which you definitely should), then you have to prioritize understanding your source environment. 

2. Plan

The next step is no surprise! Once you have a thorough understanding of your source environment and have defined your target environment, it’s time to plan.

Start by outlining each migration phase and design the necessary structures. Then, focus on setting your migration priorities which include:

• Defining your migration goals: Are you looking to consolidate tenants, clean up data, or improve collaboration? Clearly outline your objectives. 

• Aligning with your business: Involve stakeholders across the organization to ensure everyone is on the same page. This includes discussing cleanup, archiving, organizing, modernizing, testing, and training requirements. 
• Test and estimate: Run test migrations on a typical site to gauge complexity and timing.
• Identifying risks and opportunities: Assess where the most challenging areas lie and explore ways to accelerate certain portions of the migration. This might include running multiple migrations in parallel, using incremental approaches, or leveraging efficient tools like ShareGate Migrate instead of relying solely on Microsoft’s built-in options. 

A good plan also defines how to communicate with users about the transfer as well as how to proceed without imposing too many restrictions on the users’ work.  

Migrating mailboxes? What you need to know

Migrating Exchange Online (i.e. a cross-tenant mailbox migration) introduces some additional complexities into a tenant-to-tenant migration that you’ll need to think about. The first thing you need to decide is whether it makes sense to use Microsoft’s native migration tool or third-party migration tools and services.  

Although Microsoft’s native migration functionalities are helpful to Microsoft administrators, you should be aware of a few limitations before opting to use this solution for an enterprise cross-tenant mailbox migration in Microsoft 365. 

If you need to transfer more than 500 users or have a sizable volume of data you need to move for your cross-tenant SharePoint migration, Microsoft recommends using a third-party Microsoft solution, such as ShareGate’s Pro and Enterprise plans, which include mailbox migration, right out of the box. 

Although Microsoft’s native migration functionalities are helpful they have limitations that can make the process more complex and time-consuming. Here are a few examples:

• Complexity: Microsoft’s tools can be difficult to learn and use, especially for large or complex migrations. This can lead to errors, delays, and increased project costs. 

• Additional costs: Some native migration features require additional licenses, which can add to the overall cost of the project. 

These limitations can make it difficult to achieve a smooth and efficient migration using Microsoft’s native tools alone. 

Microsoft recommends using a third-party Microsoft solution provider for your mailbox migration if you need to transfer more than 500 users or a sizable volume of SharePoint data.

High-level planning for Exchange Online

Once you’ve established how you’ll be executing your migration, the next logical step is planning. Before we get into the nitty-gritty, there are a few big-picture tasks to remember: 

License management: Don’t forget to purchase the required licenses for your migration if you use a third-party solution to move your users. You need to have enough licenses to ensure that the target Microsoft 365 organization can accommodate all the mailboxes that will be migrated from the source tenant. 

Stakeholder communication: Anytime you’re doing a cross-tenant user data migration, create a communication plan to keep your users informed about the migration. Effective change management includes stakeholder engagement before the migration to inform them of any service changes, such as service integration, and what they can expect in terms of service continuity.  

M365 adoption: A successful Microsoft 365 migration goes beyond simply transferring data. Ensuring your users can effectively adopt and utilize the new environment is equally important. Here are some key considerations for M365 adoption: 

Invest in training: Develop training programs that cater to different user roles and skill levels. Ongoing training and support will help users stay updated with new features and best practices. 

Provide support: Establish a dedicated help desk or support channel to address user questions and concerns. You can also create a comprehensive knowledge base or FAQ section to provide self-service support. 

Keep users informed: Communicate openly with users throughout the migration process. Provide clear information about changes to their work environment and encourage user feedback. 

This will empower your users to leverage the full potential of the platform and drive business productivity. 

Once you have figured out how many licenses you need and have a solid communication plan, let’s walk through a cross-tenant mailbox migration step by step.  

What to do three days before “the big day” (migration day)

First, you need to prepare the domain for migration by beginning the domain verification process for the target tenant.  

Next, you’ll need to schedule the migration. For this, you’ll need to do some data mapping, creating a master list of user mailboxes you want to migrate in a CSV file that includes both the source email and the destination email.  

Then, you’ll schedule the time to live (TTL) test and disable directory sync in the source tenant. 

Migration day is here! What now?

First, you need to change the principal MX record for your domain from Microsoft 365 to a domain that is not reachable, such as unreachable.example.com. When Internet mail servers try to deliver new mail, they will queue it for a second delivery attempt every 24 hours. 

Prep the source tenant: Before the domain can be transferred to the target tenant, the original email domain must be deleted from all items in the source tenant. 

Prep the target tenant: First, ensure that the old domain has been verified in the target tenant. After removing the domain from the previous tenant, you might need to wait an hour. 

And now, the migration begins!

If you’re migrating for more than 500 users or the native migration tool doesn’t meet your organization’s needs, now’s the time to migrate with your third-party tool of choice. 

Using Microsoft’s native tool for mailbox cross-tenant migration

For some IT admins, the decision regarding whether to use Microsoft’s native migration tool is obvious. But for others, it’s not totally clear whether it will meet the needs of their organization. 

Microsoft’s native migration functionalities benefit many Microsoft administrators but relying on them for your cross-tenant migration in Microsoft 365 isn’t always the best option.  

Before you choose this method to migrate Exchange Online mailboxes, particularly for an enterprise migration, it’s important to be aware of and evaluate its limitations against your business needs.  

As part of your project management, you can do an informal risk assessment to help you decide whether to use Microsoft’s native tool for your cross-tenant mailbox migration or a third-party tool like ShareGate. Just ask yourself the following questions:  

• Is time a factor? Microsoft’s native solution has a complicated implementation process so it will take longer. 

• Do you need to filter what is migrated? Microsoft’s native solution doesn’t offer this functionality. 

• Do you have the resources and expertise within your team to write and manage the scripts for this project? Third-party tools offer no-code solutions, which not only make your migration easier but also faster. 

• Do you need to transfer the mailboxes based on delegates to keep those permissions? Mailboxes containing delegates must be moved in the same batch for permissions to migrate completely. However, when using Microsoft’s native solution, many permissions fail to migrate at all. 
• Have you considered the benefits of running concurrent migrations to accelerate data throughput and mitigate Microsoft’s throttling? Running concurrent migrations accelerates data throughput and helps mitigate Microsoft’s throttling. 

If you answered yes to any of these questions, it’s likely that the native migration tool won’t fully meet your needs.

Let’s take a look at how ShareGate can help you achieve a smooth and successful tenant-to-tenant migration no matter how large or complex the tenants that you’re migrating are.  

How ShareGate can help with mailbox migration  

ShareGate’s Migrate Pro and Enterprise plans offer Exchange Online migrations. With our tenant-to-tenant mailbox migration functionality, you can copy mailboxes right out of the box. 

• An intuitive UI that lightens the load on big migration projects with mailbox migrations that just work.  
• Simple copy selections for all mailboxes or custom groupings so you can customize your migrations as you see fit.  
• Migrate messages, attachments, and folders intact to your destination.  
• Migrating messages includes essential attributes for labeling, such as flags and importance. 
• A post-migration report that delivers the results of your migration for analysis and adjustments.   
• Easy planning for a sequenced migration with date-frames that enable you to bring over only what you need with filters that will copy 3 or 6 months of messages or set your custom timeframe.   
• Mailbox mapping that’s automated or adjustable so you can customize as you see fit. 

Easy mailbox migration at any scale 

Do you have a lot of emails to migrate? No problem!  

With ShareGate, you can sequence your migration using any timeframe that works for your business whether you need to move three or six months of messages or more.  

Migrate smart: Cover every stage of tenant-to-tenant migration 

ShareGate’s got your back every step of the way. Our streamlined workflows keep things simple and guide you through best practices. Bottom line: with ShareGate, you’ve got one tool to migrate faster and secure your tenant. 

Before migration 

In the world of IT, there’s no such thing as too much visibility into your environment. That’s especially true before, during, and after cross-tenant migrations.  

A successful migration is all about preparation. Before diving into the data transfer, it’s crucial to gain a deep understanding of your source environment.  

This is where ShareGate’s source analysis report comes in handy.  The report provides a comprehensive overview of your tenant, including:   

• The size of the environment 
• The total number of site collections 
• How many of its total sites have been inactive over the past six months 
• The overall quantity of workflows 
• A collection of many things that need your attention beneath the warnings and errors section of the report 

In addition to running a source analysis, ShareGate simplifies another critical aspect of migration: mailbox mapping. ShareGate Migrate auto-maps your mailboxes and recipients, while you review and modify those mappings to make sure everything runs smoothly at the destination. 

During migration 

Here we are, the moment of truth! Migrating with ease starts by choosing the right tool and approach. Here’s how ShareGate Migrate simplifies the process and ensures a seamless transition:

1. Run multiple migrations in parallel: ShareGate runs migrations simultaneously across different machines, accelerating data transfer throughout and mitigating throttling by splitting workloads and keeping everything running smoothly. 
2. Use an incremental migration approach: Opt for an incremental strategy to move data in phases, minimizing downtime and keeping your users productive throughout the migration. 
3. Identify and fix potential issues upfront: ShareGate helps you tackle common migration roadblocks, like problematic URLs and orphaned users, early on to avoid disruptions later. 
4. Conduct a pre-migration checkup: Use ShareGate’s pre-check report to identify any issues that can happen during migration. Get information on things like permissions, users and groups, and the site architecture.  

After migration

Time for testing and validation! While there’s no denying that data analysis is a crucial step prior to migration, you don’t want to overlook the importance of reporting after the migration is complete. At this point, it’s time to test everything out to ensure that it’s all working as it should. 

ShareGate’s Microsoft 365 migration tool provides post-migration support documentation that logs every success, warning, and error that happens during your migration. All this information is organized in an easily digestible report so you can quickly check to make sure everything migrated successfully and what areas, if any, still need some help. 

Once you’re confident that the high-level stuff is taken care of, it’s time to get into the details. With the help of detailed technical reports, you’ll be able to fill in the blanks, modify information in bulk, fix links, and ensure that your new environment is precisely how you want it. 

Our reporting tools will help you: 

• Test all workflows 
• Check user permissions 
• Create a backup of your new environment 
• Switch source to read-only mode 
• Remove access to the old SharePoint 
• Run a full crawl 
• Run a script to remove sharing links 

• Get the migration approved by key users 
• Check in with users to see how they are adjusting to their new environment 

We know that your job isn’t finished with doesn’t finish when the transfer is complete. 

Your environment will always be growing and changing as users continue to create new content. Over time, moving teams and channels will continue to be necessary to meet evolving business needs and accurately reflect how your ever-changing organization is structured.  

ShareGate gives you all the tools you need to manage these changes with ease, giving you the ability to proactively uncover emerging vulnerabilities and errors so you can nip them in the bud. Some additional key strategies to consider in the post-migration phase include:

• Future-proof governance to keep your environment compliant, clutter-free, and relevant with proper settings, policies, and workspace provisioning. Implement workspace provisioning templates to streamline the creation of new teams and sites. That way, your environment stays scalable and easy to manage. 

• Prepare for AI. Rethinking migration is critical in the era of remote work, modern AI, and employee experience. Optimize your governance strategy and policies around content management, security, and access.