Litigation Hold in Cross-Tenant Mailbox Migration Explained

Although mailbox data is generally transferable using native methods or external migration solutions, Litigation Hold in cross-tenant mailbox migration adds another dimension that must not be overlooked by IT/compliance departments.

If the mailbox is placed on Litigation Hold, then Microsoft 365 is obliged to store the mailbox data legally, for compliance purposes or investigations. Migrating such a mailbox to another tenant without adequate planning can lead to compliance issues, loss of preserved data, or legal problems.

This article discusses how Litigation Hold affects the process of cross-tenant mailbox migration, associated risks, and best practices for the enterprise IT department during the Microsoft 365 tenant-to-tenant migration process.

What Is Litigation Hold in Microsoft 365 Cross-Tenant Mailbox Migration?

Litigation Hold is a feature in Microsoft Exchange Online that allows preserving all mailbox data, including:

• Emails
• Deleted items
• Calendar entries
• Contacts
• Tasks
• Attachments
• Modified messages versions

When Litigation Hold is turned on, users are allowed to delete or modify items in a mailbox, but their copies will be stored in the Recoverable Items folder structure (specifically Deletions, Versions, and Purges).

Litigation Hold will usually be used by organizations in case of ongoing lawsuits, regulatory investigations, internal audits, HR or compliance investigations, and long-term retention requirements.

Why Litigation Hold Is Important When It Comes to Cross-Tenant Mailbox Migration

During a standard cross-tenant mailbox migration, all content of the active mailbox will be migrated to the target tenant from the source tenant. But the data kept on Litigation Hold is different from the data in the usual mailboxes.

The primary challenge

Native Microsoft cross-tenant mailbox migration processes do not automatically transfer Litigation Hold configurations or preserved Recoverable Items data in the same way as active mailbox content.

During the migration process, an organization may successfully migrate a mailbox while failing to preserve important compliance and legal data such as deleted emails, historical message versions, discovery metadata, Microsoft Purview artifacts, and retention artifacts.

As a result, the migrated mailbox may appear complete, but critical information required for audits, investigations, or regulatory obligations could be missing. This can create significant risks for legal and compliance teams.

Does Litigation Hold Migrate Automatically During Microsoft 365 Cross-Tenant Mailbox Migration?

No. While Microsoft supports cross-tenant mailbox migration for Exchange Online mailboxes, Litigation Hold settings, Microsoft Purview retention configurations, eDiscovery cases, and other compliance artifacts do not automatically migrate with the mailbox.

Organizations need to recreate or validate these compliance controls in the destination tenant. This helps to maintain legal and regulatory compliance during Microsoft 365 tenant migration.

Common Microsoft 365 Cross-Tenant Mailbox Migration Scenarios

• Mergers and acquisitions (M&A)
• Divestiture
• Tenant consolidation

In all the above cases, the assessment of Litigation Hold is mandatory prior to migration.

Technical Challenges of Litigation Hold in Cross-Tenant Mailbox Migration

1. Growth of Recoverable Items folder

The mailboxes on Litigation Hold (also referred to as Legal Hold in many organizations) generally have huge Recoverable Items folders because of ongoing accumulation of deleted items.

Large Recoverable Items folders can:

• Increase migration time
• Lead to throttling
• Generate storage quota problems
• Increase network and processing overhead

2. Hold configuration is tenant-specific

Litigation Hold settings are tied to the Exchange Online organization in the source tenant. After the migration, the target mailbox will not get the following information automatically:

• Litigation Hold status
• Hold duration
• Compliance case associations
• eDiscovery references

3. Retention of deleted/modified items

Even if the active mailbox is migrated successfully, organizations have to figure out if preserved deleted content also needs to be retained for legal continuity.

Pre-Migration Assessment Checklist

Before migrating any mailbox, IT administrators should identify all mailboxes that are under hold.

Exchange Online PowerShell to Check Litigation Hold Mailboxes

Use the following command:

Get-Mailbox -ResultSize Unlimited | Where-Object {$_.LitigationHoldEnabled -eq $true} | Select Name, UserPrincipalName, LitigationHoldDuration

Document user principal name, hold status, hold duration, mailbox size, recoverable Items size, and associated compliance cases.

This inventory should be reviewed with the legal and compliance teams before any migration activity begins.

Migration Strategies

Strategy 1: Keep the source mailbox for compliance retention

This is the safest approach for highly regulated organizations.

Process:

1. Migrate active mailbox data to the target tenant.
2. Convert the source mailbox to an inactive mailbox if licensing and retention requirements allow.
3. Maintain the source tenant for eDiscovery access until legal requirements are satisfied.

Advantages:

• Preserves original hold data
• Minimizes compliance risk
• Maintains chain of custody

Disadvantages:

• Requires continued access to the source tenant
• May increase licensing and administrative costs

Strategy 2: Recreate compliance controls in the target tenant

If the organization plans to fully decommission the source tenant:

1. Migrate the mailbox content.
2. Create the same Retention Policies, Retention Labels, or Litigation Hold settings in the target tenant.
3. Enable hold immediately after migration.

Example:

Set-Mailbox user@targettenant.com -LitigationHoldEnabled $true

Strategy 3: Use specialized migration tools

Migration tools like CloudFuze have features to support compliance-sensitive mailbox migration, such as:

• Detailed mailbox analysis
• Ability to process large mailboxes
• Pre-migration reporting
• Migration workflow aligned with compliance

In the case where there are hundreds or even thousands of held mailboxes, specialized tools can greatly lower risk.

Recommended Enterprise Workflow for Litigation Hold Mailbox Migration

Step 1: Discovery

• Identification of held mailboxes
• Creation of compliance reports
• Validation of retention requirements
• Obtain legal approval

Step 2: Pilot migration

Migration of a few held mailboxes and verification of:

• Accessibility of mailboxes
• Folder structure
• Calendar integrity
• Recoverable Items behavior
• eDiscovery search results

Step 3: Compliance validation

Post-migration process:

• Setting up required holds in the target tenant
• Running Microsoft Purview eDiscovery searches
• Comparing message counts
• Verifying application of retention policies

Step 4: Source tenant decommission

Once you get approval from your legal and compliance teams, you can:

• Release holds
• Delete inactive mailboxes
• Decommission the source tenant

Considerations Related to Microsoft Purview

The management of compliance for modern Microsoft 365 increasingly makes use of Microsoft Purview rather than individual Exchange Litigation Hold.

The IT team needs to consider eDiscovery (Standard and Premium), retention policies, retention labels, adaptive scopes, inactive mailboxes, and lifecycle management policies.

In many enterprise environments, Retention Policies may be preferred over mailbox-level Litigation Hold. This is because they provide broader workload coverage across Exchange, SharePoint, OneDrive, and Teams.

Litigation Hold vs. Microsoft Purview Retention Policies

Many enterprises are gradually shifting toward Microsoft Purview Retention Policies because they provide centralized governance across multiple Microsoft 365 workloads instead of only Exchange Online mailboxes.

Performance and Throttling Tips

Mailboxes that undergo Litigation Hold are usually larger than those of regular users. Tips for improving the migration performance:

• Reduce the number of concurrent migrations: Limit simultaneous processing of large mailboxes under the Litigation Hold.
• Keep an eye on Recoverable Items quota: Check statistics of folders: Get-MailboxFolderStatistics user@domain.com -FolderScope RecoverableItems
• Migrate during off-peak times: Avoid the effect of throttling of Microsoft 365 services.
• Perform incremental sync: An incremental pass reduces the duration of the final cutover for large mailboxes with compliance concerns.

Potential Risks Associated with Ignoring Litigation Hold in Cross-Tenant Mailbox Migration

Consequences of ignoring Litigation Hold when migrating across tenants include:

These risks could be particularly costly for industries like healthcare, finance, legal services, and government.

How Does CloudFuze Help?

For organizations migrating enterprise-level cross-tenant mailboxes, CloudFuze offers features that can assist in avoiding migration and compliance risks:

• Pre-migration mailbox assessment
• Large mailbox migration support
• Incremental sync
• Migration reporting
• Microsoft 365 tenant-to-tenant migration process flows
• Enterprise-level migration scenario support

CloudFuze can enable IT professionals to plan and implement migrations of large, compliant, or regulated mailboxes with visibility into mailbox content and migration status throughout the project.

Migrate Complex M365 Mailboxes with Complete Legal Integrity

Cross-Tenant Mailbox Migration with Litigation Hold is a legal and compliance obligation. Although Microsoft 365 offers comprehensive native migration tools, it should be understood that data that needs to be preserved during Litigation Hold has to be migrated appropriately.

The best way to do this is to:

• Find all Litigation Hold mailboxes
• Determine preservation requirements
• Select a migration method
• Recreate or maintain compliance controls
• Retention and eDiscovery validation post-migration

Moving mailboxes under Litigation Hold requires specialized tools and white-glove execution. CloudFuze automates permission mapping, deep metadata retention, and compliance validations so your legal team stays protected from Day 1. Talk to our M365 migration expert now.

Frequently Asked Questions

1. What are the essential components of a litigation hold in email systems?

Litigation hold facilitates the preservation of mailbox contents, which may be necessary for legal, regulatory, or compliance reasons. The main components of a litigation hold include emails, deleted items, message versions, mailbox properties, eDiscovery details, and retention records. Such components help the preservation of all possibly relevant information regardless of user actions such as deletion.

2. How can organizations implement a litigation hold during cross-tenant mailbox migration?

Affected mailboxes need to be placed under litigation hold before performing cross-tenant mailbox migration. Verification of litigation hold needs to take place during the process of migration. The verification will ensure that any preserved information can still be accessed in the target environment.

3. What are the best practices for ensuring compliance with litigation holds during mailbox migration?

Best practices would consist of recognizing mailboxes with litigation holds, compliance needs, validation of hold configuration before migration, testing of the migration workflow, and post-migration audits. Organizations should keep detailed logs and ensure that preserved content, metadata, and retention artifacts stay intact during the entire migration process.

4. What are common issues organizations face when managing litigation holds during mailbox migrations?

Some of the most common issues include incomplete preservation of mailbox data, lost items in the deleted list, missing eDiscovery metadata, migration problems in terms of retaining the settings, and inadequate validation after migration. These challenges can create compliance gaps and increase the risk of failing to meet legal, audit, or regulatory requirements.

5. How can organizations assess the effectiveness of their litigation hold processes during mailbox migrations?

Effectiveness can be evaluated in organizations through mailbox migration auditing, comparison between source and target data, validation of hold policies, and checking access to retained emails. Analysis of compliance reports and verification after migration ensures availability of all legally necessary information.

6. What advanced strategies should organizations consider after establishing a litigation hold for mailbox migration?

Sophisticated techniques include compliance validation automation, continuous monitoring, audits, utilization of eDiscovery tools, and proper migration documentation. In addition, organizations need to have proper governance policies for the preservation of information for the long term, compliance, and management of litigation holds across tenants.

7. How do litigation holds affect cross-tenant mailbox migrations?

Litigation holds make cross-tenant mailbox migrations more complicated because the preserved information needs to be kept safe during migration. Organizations need to take care to make sure that all the emails, deleted items, metadata, and compliance information remain intact even after migration.