Incremental Office 365 Migration: How to Migrate Only What’s Changed

What “Incremental” Actually Means Here

An incremental, or delta, migration pass looks at what’s already on the target and moves only the items added or modified on the source since the previous run. Nothing gets copied twice. For an administrator running a multi-week M&A migration, that’s the difference between a five-minute final sync and a multi-hour re-copy of terabytes of mail and files.

In practice, incremental Office 365 migration is what makes multi-week cutover windows manageable in the first place. Delta migration Office 365 tenant to tenant and incremental migration mean the same thing in this context, and both terms describe the process of comparing differences between the source state and the target state and then migrating only the differences. The objective is to make sure that there is no re-migration of information in the Office 365 migration process.

Native Support Exists, But Only for Mailboxes

Exchange Online’s cross-tenant mailbox migration already builds this in. Creating a migration batch to move mailboxes between tenants doesn’t trigger a single copy and stop. Microsoft’s mailbox move process keeps the batch in a synced state and re-syncs on a schedule, roughly once a day, so the target mailbox stays close to current without anyone re-triggering the job manually.

The real payoff shows up at cutover. Running Complete-MigrationBatch triggers one last incremental sync before it converts the source mailbox and repoints Outlook, so mail a user received an hour before cutover still lands in the right place. That’s a genuine example of incremental data sync Microsoft 365 has supported natively for mailbox moves for years now.

SharePoint and OneDrive Don’t Get the Same Treatment

Here’s where the native migration story changes. Cross-tenant SharePoint and OneDrive migrations, run through PowerShell cmdlets such as Start-SPOCrossTenantUserContentMove, do not work like mailbox migrations. Microsoft describes these moves as a one-time operation, with no incremental or delta pass available after the move. This means you cannot simply run another sync to capture changes made to the source after the migration.

That’s an important limitation for any SharePoint tenant-to-tenant project that runs for several weeks, because files on active sites can continue to change during the migration period. Microsoft also has specific licensing requirements for this feature. SharePoint cross-tenant migration is available to Enterprise Agreement customers with licensing based on the amount of data moved, while OneDrive uses a separate per-user licensing model. The feature is also not available for GCC or GCC High tenants.

What Migrating Only Changed Data Actually Requires

Before any tool, native or third-party, can migrate only what changed, a few pieces need to already be in place:

• A completed initial pass that establishes a baseline of what’s already on the target
• A reliable way to detect changes, whether through timestamp comparison, checksums, or hash-based content matching
• Consistent source-to-target mapping so the second pass lands items in the same location as the first
• The required permissions: The accounts performing the migration must have the appropriate roles and permissions for the specific Microsoft 365 workload and migration method.

Skip any of these steps, and a “delta” pass tends to behave like a full re-copy instead. These requirements are essential for Office 365 migration without re-migrating data that has already been transferred successfully.

How DRS Softech Handles This Across Every Workload

The DRS Softech Office 365 Tenant to Tenant Migration Tool provides a Skip Previously Migrated Office 365 option for mailboxes, SharePoint sites, and OneDrive accounts. Instead of treating every migration run as a completely new job, the tool can skip data that was already migrated and process the remaining or updated data on a later run. This helps skip previously migrated data Office 365 tenants have already transferred and focus on data that still needs to be processed.

For instance, if one’s mailbox is 100 GB in size and 60 GB of data volume was migrated in an earlier stage, the next run will process the remaining 40, rather than the whole mailbox. This will help if a migration takes days or even weeks and some data keeps getting added in the source tenant.

How to Perform an Incremental Office 365 Migration with DRS Softech

Steps	What to Do
Launch the Tool	Open the DRS Softech migration tool.
Connect Tenants	Connect the source and target tenants.
Select Workload	Choose Mailbox, OneDrive, SharePoint, or Teams.
Map Data	Map source data to the target destination.
Enable Skip Previously Migrated	Turn on the Skip Previously Migrated option so that data already migrated can be skipped.
Start the Migration	Start the migration and monitor its progress from the tool’s dashboard.
Run the Migration Again	Re-run the migration for new or updated data.
Review the Migration Report	Review the migration report to verify which data was successfully processed and identify any items that may need attention.

Native Tools vs. a Dedicated Migration Tool

Capability	Native Microsoft Tools	DRS Softech Tenant to Tenant Migration Tool
Incremental mailbox migration	Automatic until finalization	Yes, via Skip Previously Migrated
Incremental SharePoint migration	Not supported	Yes
Incremental OneDrive migration	Not supported	Yes
Incremental OneDrive migration	Not supported	Yes
Single dashboard for mail, SharePoint, OneDrive, Teams	No, separate tools per workload	Yes
Filtering by date, size, or file type	Limited	Yes
Active Tasks and Migration Reports	Available through workload-specific tools	Available from a centralized dashboard

Conclusion

Native Microsoft tools handle incremental Office 365 migrations with ease for mailboxes, but for SharePoint and OneDrive, each move is one-time only. A dedicated DRS Softech Tenant-to-Tenant Tool that implements the same skip-what-is-moved logic for all workloads, eliminating the need to design the migrations around the one-time-only migrations of SharePoint and OneDrive, with all of its complexity and re-copying of already-migrated data.

Frequently Asked Questions