For IT leaders and admins, tenant-to-tenant migration (also called a “cross-tenant migration”) is a critical step that your team can take to align and optimize digital resources, especially after a merger or acquisition.
Inside this article:
Tenant-to-tenant Microsoft 365 migrations are high-stakes projects triggered by mergers and acquisitions (M&A), restructuring, or compliance demands. The article divides the journey into three phases—pre-migration, execution, post-migration—highlighting exhaustive data and identity inventories as make-or-break. A 13-step playbook covers domain prep, staged mailbox moves, application reconfiguration, and post-cutover validation, each paired with best practices from Microsoft MVPs. Leaders get a tool-selection checklist, timeline-buffer advice, and early-warning signs that derail projects. The guide also explains when to engage service providers and shows how CoreView’s governance platform reduces risk before, during, and after migration.
Every migration project is unique, and your project's duration could span weeks or even years. Whether you’re migrating from Azure AD / Entra ID to the cloud or consolidating tenants, you’ll need to define a clear migration timeline with defined parameters. E.g., Who are your stakeholders – local IT teams? Department heads? C-levels? Enablement and training teams? And how many are there? Which components are you migrating? Is it mostly about user mailboxes or are you planning to move all existing services with data connected to them? How many resources will you have to support you and/or your team to perform the migration and if they have sufficient expertise and knowledge required to avoid errors and potential data loss/security breaches?
Ultimately, your migration journey will unfold through three key phases:
The pre-migration phase involves inventorying, planning and identity migration while the execution phase focuses on data migration. Post-migration encompasses user account updates, reconfigurations, and user communication.
(Please note: Given the unique nature of each migration scenario, it’s nearly impossible to create a one-fits-all guide. The approach we present here aims to cover a broad range of scenarios you’ll most likely encounter.)
Step 1: Pre-migration planning and assessment
Step 2: Set up your target tenant
Step 3: Prepare source and target tenants
Step 4: Domain configuration
Step 5: Mailbox pre-stage (for larger migrations)
Step 6: Data migration
Step 7: Update user accounts
Step 8: Reconfigure applications and integrations
Step 9: User communication and training
Step 10: Finalize migration
Step 11: Post-migration testing
Step 12: Clean up old tenant (if necessary)
Step 13: Ongoing support and monitoring
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During a recent discussion with sixteen-year Microsoft veteran Roy Martinez and nine-year Microsoft MVP Vasil Michev, we uncovered best practices for ensuring your tenant migration goes to plan. A common theme came to light: the pre-migration stage is the MOST IMPORTANT stage. It requires meticulous planning to ensure the migration goes to plan. There’s nothing particularly groundbreaking about this—BUT that stage is often overlooked or rushed.
Below are the eight best practices Roy and Vasil recommend.
A common mistake IT teams make is thinking that storage size equates to the number of items. Storage size does not necessarily equal the number of items.
During our discussion, Roy shared this example:
“Coming from a content migration perspective, when I take inventory of something—like my SharePoint site, for example—whether it's on-premises or from another tenant site, I might see that it has ten gigabytes (GB) of data according to my storage reports. I might then assume that data generally moves at roughly five GBs an hour and calculate that it will take me two hours to move that data.
However, what I might not have considered is that those ten GBs of data could consist of five million different items—rather than just ten one-GB items. This is a significant factor when it comes to throughput! When you're moving data across cyberspace, moving ten one-gigabyte 'bricks' of data might take some time, but it's considerably easier than moving 5,000,000 .1 gigabyte bricks.”
In other words, it's more important to understand the total number of individual items in the SharePoint object model than the total GB size of your storage.
The number of items (or, “bricks”) of data you’re moving can significantly impact your migration throughput. The more items you have, the more difficult it will be to migrate them. This underscores the importance of understanding (and documenting) the number of GBs and individual items you have.
Join Roy and Siam for “Mission 365: five strategies to guide your Microsoft 365 tenant migration project” for best practices when building your migration plan. Learn more here.
When taking stock of your items and data, be sure to inventory your identity data. That includes all identity powers—so, not just access to mailboxes and files, but also access to Line of Business (LOB) processes, automation, and third-party integrations.
This is a commonly overlooked aspect. But, failing to consider these can potentially break integrations with on-premises and Software as a Service (SaaS) apps.
Read Vasil’s thoughts below:
"A common mistake to avoid when going through a migration is failing to gather a proper inventory of service principals, managed identities, and integrated applications. Overlooking the identity aspects of a tenant-to-tenant migration can lead to users ending up with no access to the HR system, or some automated/critical business processes being broken."
In essence, a comprehensive inventory of both your data and identity powers is crucial in avoiding potential issues during the migration process.
Different tools have different strengths. You won't always find a single migration tool that fits all your needs. And, if the tool you choose fails to cover certain aspects of your migration, you will likely face complications down the line, including cost increases.
For example, selecting a tool that does wonders in migrating Exchange data but fails to migrate solutions built on top of SharePoint Online (SPO) or data held in Preservation Hold Libraries, can lead to complications.
You may even consider using Microsoft’s native tools like Administrative Units. These are helpful if you need to assign a subset of your users to an AU. Then, you can delegate administrative permissions for that AU to specific IT admins who are responsible for that group of users—allowing you to manage and migrate each AU separately and providing a more controlled and organized migration process.
However, it's important to note that while AUs can help segment your migration process, they don't inherently facilitate the migration of data or services from one tenant to another. You'll still need to use appropriate migration tools and strategies to move your actual data.
For IT managers and system administrators managing multiple tenants in Azure AD, it's crucial to understand the complexities involved. Read our handbook for managing multiple tenants in Azure AD for detailed insights and strategies.
When creating your migration timeline, be sure to add buffer time to it to account for any forgotten inventory items during the pre-migration stage.
Underestimating the time required for the migration is a common mistake and, inevitably, you will forget to inventory some sets of data.
The purpose of pre-migration inventory is to understand what you're trying to move so that you don't move things you don't need. One of the biggest advantages of pre-migration is identifying what won't work in the target that you've defined.
For example, you may be using a custom solution that’s not available in the target tenant or your SharePoint site may have data tied to a mechanical solution that won’t work in the target tenant. Be sure to devise a strategy for how you are going to migrate those particular items as it will likely require some sort of transformation to fit into the new system.
See how CUNY leverages CoreView Virtual Tenants™ to deliver Microsoft 365 to 243,000 students and more than 40,000 staff and faculty
Your migration approach should be based on your pre-migration inventory to ensure it best suits your organization's needs and resources.
You have four options: the Big Bang approach for a single event migration, the staged migration for gradual data migration, the phased migration that would happen in batches, and the rapid switch approach for partial pre-staging and migration.
For example, if you're a small company that got acquired by a big company (and all you ever did was keep a bunch of files in folders on a file server), the Big Bang approach might be suitable for you. However, if you're moving from folders in a file system to SharePoint, a phased approach might be more appropriate.
Organizations often do not take time to create a good data and file structure before the migration. Instead, they’ll pick up everything in the original tenant and dump it into the new one—resulting in a cluttered mess.
Cleaning up your data prior to migration can prevent clutter and ensure a smoother migration process.
Here’s Roy again,
“At my prior organization, I was tagged to help the marketing department migrate their foldering structure from SharePoint to Teams. The goal of this was to make it easier for them to do all of their work out of Teams.
“But, the folders had super old data in them—campaign data from 2016, old logos, etc. We migrated everything.
“Ultimately, the team ended up having to clean up the NEW foldering system after the fact. It took a couple of weeks to fully migrate the data over. It would’ve taken the same amount of time to just clean up the files before the migration—and we would’ve ended up with a better end product.
“In hindsight, we should’ve done a full data clean up before the migration. Strip out the old stuff, archive it, and don’t even move it over in the first place.”
Migrate your identities first and foremost—even if you're not logging into the target tenant yet. Everything that gets moved in an identity-focused security model needs to be owned by someone. Not only should you understand what you're moving (and why and where and how you’re moving it), but you should also understand who will own everything once it is moved.
Identity migration usually either comes very first or very last. In an identity-focused security model, everything—every piece of content, document, SharePoint site, mailbox, and team that gets moved must be owned by someone.
For instance, let’s say “Joelle” owns “Document X” in Tenant A and that document is moved to Tenant B. It must be owned by someone in Tenant B as well. You should have a pre-instantiated user object ready for “Joelle” in Tenant B, even if she hasn't started logging in there yet.
To accomplish this, you may consider using Microsoft Administrative Units to help manage and migrate specific groups of users separately.
So, to sum it up, prioritizing the migration of identity data ensures that every piece of content, document, SharePoint site, mailbox, and team has an owner—meaning you prevent potential access issues.
If you’re going with a rapid switch migration approach, be sure to pre-instantiate users in the target tenant. Then, at a predefined time, switch those users over.
This approach is particularly useful when moving user identities.
But, be careful not to switch over everything before all the other workloads (such as email, content, and sites that users need to access to exist) have been migrated into the target tenant.
Remember that a user can represent not only a person but also a device or a mailbox, among other things. However, usually that user represents a human being that needs to work!
So, let’s go back to the previous example.
“Joelle” exists on Tenant A and we need to move her to tenant B. We could either move Joelle's user account to Tenant B and notify her to log in with new credentials starting tomorrow. However, she won't be able to access her usual information until we've completed the migration, meaning her work is disrupted.
The other option is to choose a more hybrid approach and pre-instantiate Joelle in Tenant B. She keeps working at a normal pace and can access all of her files. Then, at a predetermined moment, we’d switch everything over to the new setup.
What is “pre-instantiation? In a tenant-to-tenant migration in Microsoft 365, you might pre-instantiate user accounts in the target tenant. This means you would set up the user accounts in the new tenant before you start moving data. This way, when the data migration takes place, each piece of data already has an owner in the new tenant, which can help ensure a smoother transition and maintain proper access controls and permissions.
Be sure not to underestimate the compliance aspects of a tenant-to-tenant migration.
Your compliance needs and obligations might require you to move or retain prolonged access to data in the original tenant, including files protected by sensitivity labels/Information Rights Management (IRM).
Neglecting this can mean you risk breaking compliance requirements or losing access to the protected data.
For example, imagine a scenario where you overlooked the retention policies and sensitivity labels during the migration process. This oversight could lead to crucial data being inadvertently lost or rendered inaccessible, causing a significant disruption to your operations and potentially violating compliance requirements.
Never assume that things will "just work".
Discover 10 Microsoft 365 tenant management best practices for Enterprise IT Managers.
There may be a variety of business needs that trigger a Microsoft 365 tenant consolidation project. As an IT leader, it's essential for you and your team to gain a clear understanding of these triggers. Not only does it unveil the urgency of these migrations, but it also reveals the significant benefits they can offer your organization.
There are many variables that may impact your migration plan—and no single plan or set of instructions can encompass everything. So, while we focus strictly on the tenant-to-tenant migration process in this article, the reasons (and processes described further down below) may be applicable to other types of migration.
Below are the typical triggers for migrations.
When organizations undergo mergers, acquisitions, or divestitures, they often inherit different Microsoft 365 tenants with distinct configurations, user bases, and collaboration tools. Migrating to a single tenant after M&A activity allows you to integrate operations seamlessly, foster a unified company culture, and enhance collaboration among all teams—even across different entities. A consolidated tenant can also streamline license management and reduce administrative overhead.
If your organization is undergoing restructuring or internal reorganization, you may need to reevaluate your IT infrastructure to eliminate redundancies and streamline processes. Merging multiple tenants into one facilitates a smoother transition during these transformations, helping to realign teams, resources, and communication channels. This leads to increased efficiency, reduced costs, and a more cohesive digital ecosystem.
In some industries, data security and compliance regulations are paramount. When you consolidate tenants, you’re centralizing control over security policies, data access, and compliance measures. A unified tenant simplifies audits, monitoring, and enforcement of security protocols, ensuring sensitive information is safeguarded and regulatory requirements are met.
If you have multiple tenants, your organization may be underutilizing resources or overspending on licenses. By consolidating into a single tenant, companies can optimize the allocation of licenses, eliminate redundant subscriptions, and negotiate better licensing agreements with Microsoft. This can lead to significant cost savings in the long run.
Operating on different tenants can create silos that hinder seamless collaboration among employees, partners, and clients. A unified tenant can help foster better communication, data sharing, and teamwork across your organization. Users can access shared resources, calendars, and documents easily, driving productivity and innovation.
If your organization has multiple tenants, the IT department may face challenges governing and enforcing consistent policies and procedures. Migrating to a single tenant provides a way to standardize IT processes, security measures, and governance policies, leading to improved management and support capabilities.
For companies experiencing rapid growth or expansion, you may outgrow your existing Microsoft 365 tenant(s). Migrating to a new, scalable tenant allows organizations to accommodate an increasing number of users, applications, and data while maintaining optimal performance.
A Microsoft 365 tenant migration project can open doors for a myriad of business initiatives, propelling you and your organization towards unparalleled success. By unifying disparate tenants into a harmonious digital ecosystem, your business can unlock a host of transformative outcomes that redefine collaboration, productivity, and innovation.
Take a look at the potential outcomes below to determine how the project may impact your organization.
Consolidating Microsoft 365 tenants can streamline communication, data sharing, and collaboration across your organization. With all teams operating within a single tenant, employees can access shared resources, calendars, and documents seamlessly, eliminating silos and fostering a culture of collaboration. This enhanced teamwork drives productivity as information flows effortlessly, and decision-making becomes more agile.
By migrating to a single tenant, your organization can optimize its resource allocation, making the most of available licenses and subscriptions. Redundant or underutilized licenses can be identified and reallocated, leading to cost savings and improved license management. Moreover, centralized resource management allows IT teams to deploy updates, patches, and security measures more efficiently.
Operating on multiple tenants may result in fragmented security policies and compliance measures. With a unified tenant, your organization can enforce consistent security protocols, ensuring data protection and compliance with industry regulations. Centralized monitoring and management facilitate timely identification and resolution of security threats, reducing the risk of data breaches.
The migration process presents an opportunity to streamline IT governance and management processes. Your IT team can standardize policies, configurations, and procedures across the organization, simplifying administration and support tasks. Having a unified tenant enhances visibility, allowing your administrators to make data-driven decisions and proactively address potential issues.
A single tenant environment offers your users a seamless experience as they access familiar tools and resources. With uniform login credentials and domain settings, employees can collaborate effortlessly across departments and geographical locations. Providing a consistent user experience can enhance user satisfaction and reduce the need for additional training.
Migrating to a new, scalable tenant prepares your organization for future growth and technological advancements. As businesses expand, a unified environment can accommodate an increasing number of users and applications without compromising performance. By preparing for the future, your organization can stay agile and adapt to evolving market demands.
Consolidating tenants can enable your organization to implement consistent data management and retention policies. IT teams can centralize data backup and recovery processes, ensuring business continuity and mitigating the risk of data loss. A well-structured data management strategy enhances data accessibility and retrieval, empowering your users to make informed decisions.
A single tenant environment helps facilitate seamless collaboration with your external partners, vendors, and clients. By sharing resources and documents within the same tenant, you can help break down collaboration barriers and build stronger relationships with external stakeholders—enhancing collaboration, fostering innovation and driving business growth.
A unified Microsoft 365 environment reduces the complexity of IT support and training. Your IT team can focus on a single set of tools and configurations, making troubleshooting and issue resolution more efficient. End-users benefit from simplified training programs, as they navigate familiar applications and workflows within the unified tenant.
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By carefully evaluating the features and limitations of certain tools, your business can make informed decisions when choosing the best migration tool that aligns with your unique requirements, ensuring a successful and smooth transition to a new Microsoft 365 tenant.
Here are ten considerations to help you in your evaluation.
Migration Scope
Ideal features: Look for a tool that supports comprehensive migration, including mailboxes, SharePoint, OneDrive, AND Teams data.
Limitations: Some tools may have limitations on the types of data they can migrate, leading to a need for multiple tools or manual migration.
Performance
Ideal features: Opt for a tool with high-speed data transfer and scalability for large-scale migrations, minimizing downtime and disruptions.
Limitations: Certain tools may experience performance issues or throttling during migration, leading to potential delays.
Customization and flexibility
Ideal features: Choose a tool that offers advanced customization options to tailor the migration process according to specific organizational needs.
Limitations: Some tools may have limited flexibility, forcing businesses to adopt a one-size-fits-all approach.
User-friendly interface
Ideal features: Prioritize tools with an intuitive and user-friendly interface for easy migration planning and execution.
Limitations: Complex tools with steep learning curves may require additional training for IT administrators.
Data security
Ideal features: Ensure the migration tool provides robust data security features, including encryption and compliance measures, to protect sensitive information.
Limitations: Inadequate data security features may expose data to potential risks during migration.
Cost and licensing structure
Ideal features: Evaluate the total cost of ownership and licensing structure of the tool to align with the organization's budget.
Limitations: Some tools may have higher initial investment or ongoing licensing costs that may not align with the organization's financial constraints.
Support and training
Ideal features: Look for tools with comprehensive technical support and training resources to assist IT administrators during the migration journey.
Limitations: Lack of adequate support may result in challenges or delays during the migration process.
Automation and monitoring
Ideal features: Consider tools with automation capabilities to streamline migration processes and real-time monitoring for tracking progress.
Limitations: Limited automation features may result in manual intervention and slower migration times.
Scalability
Ideal features: Select a tool that can handle migrations of varying sizes, from small organizations to large enterprises.
Limitations: Some tools may not scale well, leading to inefficiencies for larger migration projects.
Data integrity
Ideal features: Prioritize tools with data integrity checks and validation to ensure that all information is accurately transferred.
Limitations: Inadequate data integrity features may result in data loss or corruption during migration.
Service providers play a critical role in facilitating successful migrations. They bring expertise, specialized tools, and experience to streamline the migration process and mitigate potential challenges. These providers collaborate closely with organizations to assess their unique requirements and craft tailored migration strategies that align with their specific business goals.
By carefully selecting the right service provider, your organization can leverage external expertise to streamline the migration process, achieve business objectives, and embrace the transformative possibilities that come with a successful Microsoft 365 tenant-to-tenant migration.
MSPs, maintain customer confidence in your security protocols. Read why it’s crucial for MSPs to maintain baseline configuration.
To ensure a successful and smooth migration process, there are multiple components that will need attention. Before you start a migration project, review the comprehensive checklist below, or download a copy of the full checklist here.
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It's important to remain aware of potential challenges when undergoing a tenant migration project.
How does a migration project affect other people in your organization? For the end-users, it may mean as “little” as not being able to log in, downtimes, lots of no-delivery emails. Or, you could end up with lots of data loss and, ultimately, apprehension to change and adoption to new technologies.
Let’s jump into the risks.
During the migration process, if data isn’t migrated correctly or some files are accidentally overlooked, vital information may be lost, leading to potential disruptions in your business.
Another risk is the possibility of service disruptions during the migration. For instance, if the migration process encounters technical issues or conflicts with existing configurations, it could result in temporary unavailability of critical applications and services, impacting productivity and causing frustration among users.
During migration, sensitive data may be exposed to unauthorized access if proper security measures aren’t implemented. This could lead to data breaches or compliance violations, putting the organization at risk of financial and reputational damage.
Sometimes, the project may require additional resources, support, or licensing, potentially straining your organization's budget. Inefficient resource allocation may occur if your organization fails to allocate the right resources for the migration—leading to delays, overspending, and reduced productivity.
New processes and platforms may cause users to become frustrated. This is especially true when a migration process isn’t well-communicated or when users struggle to use the new tools, ultimately decreasing morale and adoption.
Extended downtime can occur if migration issues cause prolonged disruptions, impacting your business operations and potentially resulting in revenue loss.
Compliance violations are a serious consequence of migration gone wrong, as mishandling sensitive data during the process could lead to legal and regulatory consequences.
A cross-tenant migration in the Microsoft 365 ecosystem is a strategic move that aligns IT infrastructure with the dynamic needs of modern businesses. Understanding the diverse triggers for such migrations empowers IT leaders to make informed decisions that optimize collaboration, enhance security, and drive overall efficiency.
Through meticulous planning, thoughtful execution, and leveraging the step-by-step guide and supplemental checklist, your organization can successfully navigate the tenant-to-tenant migration journey and unlock the full potential of a unified Microsoft 365 environment.
Before you begin your migration journey, it may be worthwhile to consider using a Microsoft 365 management platform to help your team manage the migration more effectively. Platforms like CoreView, although not direct migration tools, offer crucial capabilities for assessing application performance, enforcing security protocols, optimizing license usage, and streamlining user provisioning per Microsoft 365's best practices.
With CoreView, you can dig deep for insights and analytics to enhance collaboration, productivity, and resource utilization, leading to data-driven decisions and tenant performance optimization. Easily monitor user activity, mailbox usage, and application performance to ensure a smooth transition. By using our pre-built policies and automation options, your team can manage user accounts, permissions, and resources in the target tenant, while automated features aid the IT division with routine tasks, thus improving operational efficiency. This ensures minimal disruptions and data integrity during the migration process. Plus, CoreView’s capabilities extend beyond migration to support ongoing operations in your Microsoft 365 environment.
With its intuitive interface, you can automate processes like:
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Like the article? Send your feedback to me at kasia.nowicka@coreview.com. Ciao!
