What Is Microsoft 365 Migration and How Does It Work?

What Is Microsoft 365 Migration?

Microsoft 365 (Office 365) migration is the process of migrating users’ or employees’ data into, out of, or between Microsoft 365 environments. The source may be an on-premises Exchange server, an IMAP-based system, a third-party platform such as Google Workspace, or another Microsoft 365 tenant. In contrast, Microsoft tenant to tenant migration moves user data between two existing Microsoft 365 tenants. Microsoft supports it for mergers, acquisitions, divestitures, and internal reorganizations.

Why Do Businesses Choose Office 365 Migration?

Most organizations migrate for one of two reasons. First, it may be that some organizations want to move from old Exchange servers to Microsoft Exchange servers, whereas others need to reorganize tenants after a merger, acquisition, or divestiture. The following reasons are the expertise that makes it professional and secure:

• Users can easily access Microsoft 365 data from any device, which keeps hybrid work flexible.
• Microsoft maintains the cloud services; consequently, server patching and upgrades no longer burden IT teams.
• Controls like data loss prevention are plan-dependent, so admins must configure them under the shared responsibility model.
• Admins adjust users and licenses as headcount changes, without provisioning additional hardware.
• A subscription replaces much of the on-premises hardware burden, although savings vary by environment.
• Mergers, acquisitions, and divestitures require tenant-to-tenant data moves, and MSPs consolidate client tenants likewise.

Types of Microsoft 365 Migration

Microsoft 365 (Office 365) migration is generally classified into 2 categories. First, the main migrations for tenant to tenant and external-to-Microsoft 365. The second is workload migrations like Exchange Online, OneDrive, and SharePoint.

1. Main Migration

a. Tenant to Tenant Migration: migrating data between two different tenants.

• Single Event Migration: transferring all users and data in one cutover event. It works well for small to medium businesses.
• Phased Migration: migrating users in batches, which spreads the overall data. It works fine for large enterprises.
• Tenant Move/Split: Moves a subset of users while the remaining users stay in the source tenant. It is common in divestiture scenarios.

b. External-to-Microsoft 365 Migration: Migrate data from an external platform into a Microsoft 365 tenant.

• Google Workspace: Mailboxes follow a dedicated Exchange Online migration path.
• File Shares: Moves on-premises shares into SharePoint or OneDrive.
• Dropbox and Box: Moves cloud storage content into Microsoft 365. Migration Manager handles these transfers as well.
• Other Sources: Exchange Server, IMAP-enabled systems, and PST files have separate Exchange Online migration paths, while Slack has a dedicated Slack-to-Teams migration tool.

2. Workload-Wise Migration: Using Professional Tool

• Exchange Online: Migrates email, calendars, tasks, and contacts. The method depends on the source, and IMAP copies email only.
• OneDrive: Moves user files into OneDrive or between tenants. Admins should verify that sharing permissions carry over.
• SharePoint: Moves sites and document libraries into SharePoint Online. Cross-tenant moves follow a separate Microsoft process.
• Teams: The Orchestrator moves Teams chats and meetings. Meetings require chats and mailboxes in the same batch.

How Does Microsoft 365 Migration Work?

Migrations work in six steps covering the whole phases from discovery and planning to migration and its validation. The following steps show all the steps:

Step 1: Discovery and Planning
First, assess the complete data, such as users, mailboxes, OneDrive, SharePoint, Teams, licenses, etc and required dependencies for the migrations.

Step 2: Domain and License Preparation
Next, prepare target users, assign required licenses, plan domain transfer, and configure MailUser objects with the necessary attributes for identity mapping and mail routing.

Step 3: Establishing Secure Authentication
Afterward, configure the migration application, OAuth permissions, Exchange Online migration endpoint, and organization relationship to establish secure communication between both tenants.

Step 4: Data Mapping and Batch Creation
Subsequently, map source users to target MailUsers, verify required attributes, and create migration batches based on the selected migration strategy.

Step 5: Migration Execution
Then, migrate supported mailbox data, while OneDrive, SharePoint, and Teams workloads follow their respective migration methods, dependencies, and processing requirements.

Step 6: Validation and Cutover
Finally, validate migrated data, permissions, etc.

Microsoft Tenant to Tenant Migration Checklist

Before migrations, make sure to confirm and verify all the prerequisites. Otherwise, sync conflicts, throttling, or data loss may occur during migration.

1. Complete a Full Source Tenant Inventory: First, document every mailbox, distribution list, OneDrive volume, and SharePoint site. This inventory establishes your post-migration validation baseline.
2. Prepare and License the Target Tenant: Assign sufficient licenses matching source user count. Additionally, provision Exchange Online, SharePoint, and Teams services beforehand.
3. Verify Domains on Both Tenants: Next, verify custom domains in the target tenant. Since domains function exclusively per tenant, plan handoff timing carefully.
4. Review Administrative Roles and Permissions: Confirm Global Administrator access and required Azure AD permissions. Without proper roles, migration batches fail to initialize.
5. Identify Mailbox Holds and Retention Policies: Furthermore, check for litigation holds or retention policies. Mailboxes under hold require special handling before migration.
6. Plan DNS, MX, DKIM, and DMARC Changes: Additionally, map DNS record updates, including MX and DKIM entries. Preparation minimizes downtime during final cutover.
7. Freeze Non-Essential Mailbox Changes: Reduce configuration edits and forwarding rule changes. Ongoing modifications often cause sync conflicts mid-migration.
8. Create a Full Data Backup: Therefore, back up mailboxes, OneDrive files, and SharePoint content. This backup provides a fallback restore point.
9. Test Authentication and Connectivity: Validate authentication between both tenants beforehand. Confirm connectivity succeeds before initiating full batch migration.
10. Run a Small Pilot Batch First: Finally, migrate a small test group initially. This surfaces configuration issues while impact remains limited.

Manual Microsoft 365 Cross-Tenant Migration Methods

In this section, we will discuss two manual methods to perform migration between tenants. You can choose the approach that best fit for your migration task.

Method 1: Native Microsoft Migration (PowerShell + Exchange Online)

Microsoft supports native cross-tenant Exchange mailbox migration through Exchange Online PowerShell and MRS. Administrators use migration endpoints, organization relationships, target MailUsers, and migration batches.

Prerequisites to Verify First

• Appropriate Exchange Online licenses are assigned to source and target users.
• Cross-Tenant User Data Migration licenses are assigned to migrating users.
• Target users are prepared as MailUsers with required migration attributes.
• Mailboxes on any type of hold cannot be migrated natively.
• Required administrative permissions and a mail-enabled security group are configured.

Steps:

1. Sign in to the Microsoft 365 Admin Center, proceed to Domains snf verify.
2. Create a client secret and grant the required Exchange Online permissions.
3. Configure organization relationships between the source and target tenants.
4. Then, create a mail-enabled security group and add the users to be migrated.
5. Now, create target MailUsers and configure the required Exchange attributes.
6. Create and validate the migration endpoint using Exchange Online PowerShell.
7. Prepare the CSV mapping and create a migration batch with New-MigrationBatch.
8. Start and monitor the migration until the mailboxes are successfully synchronized.
9. Complete the migration and update mail routing/DNS records as required.

Limitations to Consider

This method requires careful configuration, PowerShell administration, correct identity mapping, licensing, and compliance checks. Mailbox holds and Microsoft service limits can also prevent migration.

Method 2: PST Export and Import Migration

PST migration separates mailbox export from import, allowing administrators to move email data without establishing a direct mailbox migration relationship between tenants.

Steps for Office 365 migration:

1. Verify prerequisites by verifying source/target accounts, licenses, permissions, and available storage.
2. Now, proceed to Exchange Powershell and connect the admin account.
3. Then, run this command in it:

New-ManagementRoleAssignment -Role “MyMailboxImportExport” -User Administrator



4. Proceed to the Microsoft Purview Portal or eDiscovery.
5. Then, create the Content Search, then import the mailbox and search it,
6. Export mailbox data from the source tenant into PST files.
7. Verify the PST files and organize them according to the target users.
8. Sign in to the Microsoft 365 Admin Center using appropriate administrator permissions.
9. Open the Microsoft Purview portal and go to the Import solution.
10. Create a new PST import job and select the required upload/import method.
11. Upload the PST files and prepare the mapping CSV for the destination mailboxes.
12. Start the import process and wait until its completion.
13. Verify that the migrated data is successfully present in destination.

Limitations to Consider

PST migration requires separate export and import stages. Microsoft documents a 20-GB recommended PST file limit, and import speed depends on the environment and method used.

Professional Tool for Microsoft 365 Tenant-to-Tenant Migration

When bulk migration or multiple mailboxes are involved, manual PowerShell scripting simply can’t keep pace. This is where the SysInfo Microsoft 365 Tenant to Tenant Migration Tool proves useful. It can handle bulk mailbox migration, preserve folder hierarchy, smart deduplication, date-range filtering, incremental sync support, and mailbox mapping, all within a single interface. Additionally, it exports and splits resultant PST files for added flexibility.

Steps to Migrate Microsoft 365 Tenant-to-Tenant:

1. Download and launch the tool. Then, click Copy Mailboxes to begin.
2. Choose your authentication method and sign in to the source tenant account.
3. Next, select the required source tenant user IDs, then click Continue.
4. Now, sign in to the destination tenant and map the source user IDs to their target accounts.
5. Then, you can apply filters (date range, deduplication, folder type, etc.) and click Start Migration to begin the transfer.

Note: For detailed steps, check the software guide for Microsoft Cross-Tenant Migration. It gives you clear instructions with proper screenshots.

Why Choose SysInfo Migration Tool for Microsoft 365 Migration?

It provides several features for complex filtering and more. These features make the tool reliable and safe:

• Emails, attachments, contacts, and calendar metadata remain intact throughout the process.
• Bulk processing & incremental sync support. Preserved folder structure across source and target.
• Move Email, OneDrive, Teams, SharePoint, and more between different tenants on Microsoft 365.
• Smart deduplication feature removes duplicate mailbox, SharePoint, and OneDrive items before migration to ensure uniqueness of data.
• Apply Advanced Mapping: Map source user IDs to target accounts individually or in bulk, ensuring accurate delivery.
• Provides Local Installation: Works on Windows and Mac OS

Conclusion

In this blog, we’ve explained the manual methods and a professional alternative for Microsoft 365 migration. To begin with, manual approaches require Exchange Online PowerShell scripting, complex endpoint configuration, and repeated administrative effort. Moreover, large mailboxes experience API throttling and synchronization timeouts, making the process unreliable for bulk Microsoft 365 tenant to tenant migration. Conversely, a professional tool resolves this through direct migration with bulk processing, built-in filtering, and advanced deduplication functionalities. Additionally, you can use the demo version to test its features.

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