October 21, 2026
What MigrationWiz customers need to know when moving mailboxes that are subject to legal holds, retention policies, or regulatory requirements.
Microsoft 365 migrations are often treated as a data-movement exercise: move the mailbox, move the messages, validate the results, and move on.
But what happens when a mailbox is subject to a legal hold or retention policy?
That’s where migration planning becomes more important.
Legal holds and retention policies do not migrate with mailbox data. They are configured at the tenant level in Exchange Online or Microsoft Purview, rather than being part of the mailbox content itself.
For organizations moving mailboxes between Microsoft 365 tenants—particularly during an M&A or tenant consolidation project preserving that data requires more than simply migrating the mailbox.
The Data Moves. The Policies Don’t.
MigrationWiz can migrate mailbox content, including messages, calendar items, contacts, tasks, folders, and other supported mailbox data. Archive mailbox content and Recoverable Items can also be migrated using the appropriate MigrationWiz projects.
The policies governing that content are different.
Litigation Holds, eDiscovery holds, Microsoft 365 retention policies, retention labels, and Exchange MRM policies are configured separately in the source environment. They must be reviewed and recreated in the destination tenant as part of the migration plan.
That distinction is critical.
If a mailbox is protected by a hold in the source tenant but the corresponding protection isn’t established in the destination, migrated content—particularly content in Recoverable Items—could become subject to deletion.
Start With a Hold and Retention Inventory
Before migrating a mailbox subject to legal or regulatory preservation, identify every hold and retention mechanism affecting it.
That may include:
- Litigation Holds
- Microsoft Purview eDiscovery holds
- Microsoft 365 retention policies
- Retention labels
- Exchange MRM retention policies
- Inactive mailboxes
The goal is to understand not only which mailboxes are protected, but why they are protected and what preservation requirements apply to them.
This inventory should be reviewed with Legal and Compliance before the migration begins.
For M&A migrations, this step is particularly important. Different source companies may have different preservation policies, making it easy to overlook a mailbox or assume that the destination tenant’s existing policies provide equivalent protection.
Recreate Protection Before Moving the Data
One of the most important principles for migrating a mailbox on hold is simple:
Establish the appropriate protection in the destination before migrating the protected data.
For example, Litigation Hold should be enabled on the destination mailbox before migrating its Recoverable Items. Likewise, required eDiscovery cases, retention policies, and labels need to be recreated in the destination environment.
This sequencing matters because destination policies can affect migrated data as soon as it arrives.
Retention policies can calculate an item’s retention age based on its original date. That means an email that is several years old doesn’t necessarily become “new” simply because it was migrated yesterday. If a destination policy is configured to delete older content, migrated messages could be affected shortly after they arrive.
Before migration, review destination retention policies and determine whether incoming mailboxes need to be excluded until the appropriate preservation controls are in place.
Don’t Forget Recoverable Items
Recoverable Items deserves special attention when migrating mailboxes under legal hold.
The Recoverable Items folder can contain deleted and previously modified content that must be preserved. MigrationWiz supports migration of Recoverable Items for supported Exchange and Microsoft 365 migration scenarios through a dedicated project.
If that data is migrated into a destination mailbox without the appropriate hold or retention configuration, it can eventually be purged.
For organizations with significant legal or compliance requirements, the migration plan should therefore account for three separate things:
The mailbox. The archive. The Recoverable Items.
Treating the primary mailbox migration as the complete preservation process can leave important data behind.
What About Inactive Mailboxes?
Inactive mailboxes require additional planning because they don’t have an active user account associated with them.
An inactive mailbox may have been preserved because of a hold or retention requirement after the associated user account was deleted. According to the source material, these mailboxes need to be recovered or restored to an active mailbox before they can be migrated through the standard process.
Include inactive mailboxes in the initial discovery process rather than discovering them after the migration is underway.
Keep the Source Until Legal Signs Off
A successful data migration doesn’t automatically satisfy an organization’s legal or regulatory obligations.
MigrationWiz moves data from one environment to another. It isn’t, by itself, a forensic collection or legally defensible preservation process. Organizations involved in active litigation or regulatory matters should involve Legal and Compliance in the migration plan and determine what additional preservation or eDiscovery processes are required.
That may also mean keeping the source mailbox—or even the source tenant—intact until Legal confirms that preservation requirements have been satisfied.
Don’t decommission the source simply because the migration has completed.
Plan for the EWS Transition
The transition away from Exchange Web Services adds another consideration for organizations planning migrations involving held mailboxes, archives, or Recoverable Items.
Microsoft has announced that EWS in Exchange Online will begin being disabled in October 2026, with full disablement scheduled for April 2027. Microsoft Graph is the strategic replacement, but Microsoft has identified remaining capability gaps for some migration scenarios.
If your migration includes mailboxes under legal hold, large archives, Public Folders, or Recoverable Items, review the current support for your specific migration scenario before scheduling the project.
The important point is to plan early. Compliance-sensitive migrations can involve additional discovery, approvals, testing, validation, and source-retention requirements that shouldn’t be left until the final migration window.
A Simple Planning Framework
For MigrationWiz customers, the process can be summarized in a few steps:
- Identify.
Inventory every hold, retention policy, archive, Recoverable Items requirement, and inactive mailbox. - Involve Legal.
Confirm preservation requirements and obtain approval for the migration approach. - Prepare the destination.
Recreate the required holds and retention policies before protected data arrives. - Migrate the data.
Move the mailbox, archive, and Recoverable Items using the appropriate MigrationWiz projects. - Validate.
Confirm data, mailbox sizes, item counts, holds, and applicable eDiscovery results. - Keep the source.
Don’t decommission the source environment until Legal and Compliance confirm that preservation requirements have been met.
The Bottom Line
Migrating a mailbox under legal hold isn’t simply a matter of moving its contents.
The data moves. The protection doesn’t.
Successful migrations require the destination environment to be prepared before protected data arrives, Recoverable Items to be accounted for, inactive mailboxes to be identified, and Legal and Compliance teams to remain involved throughout the process.
With the right planning, MigrationWiz can help move the supported mailbox data while your team focuses on preserving the policies, controls, and documentation that surround it.
Identify the holds. Prepare the destination. Migrate the data. Validate everything. Keep the source until Legal signs off.