A Complete Guide to Migrating Mailboxes to Microsoft 365 in a Hybrid Deployment

To migrate mailboxes from on-premises Exchange to M365/Exchange Online is a critical step for businesses moving to the cloud. A hybrid deployment facilitates seamless coexistence between on-premises and cloud environments, enabling mailbox migrations with minimal disruption. This article outlines the key steps, prerequisites, and troubleshooting tips to ensure successful mailbox migration.

What Is a Hybrid Deployment?

A hybrid deployment bridges on-premises Exchange and M365, allowing:

• Mailboxes to move between on-premises and cloud environments.
• Retention of a unified email experience for end users.
• Gradual migration over time instead of an all-at-once transition.

Hybrid deployments support remote mailbox move requests through the Mailbox Replication Service (MRS) and its proxy, MRSProxy. These setups are ideal for long-term coexistence scenarios.

Prerequisites for Mailbox Migration

Before starting a mailbox migration, ensure the following:

Technical Requirements

1. Hybrid Deployment Configuration:

• Verify that your hybrid deployment is configured correctly. Refer to Microsoft’s Hybrid Deployment Prerequisites for details.

2. Mailbox Replication Service Proxy (MRSProxy):

• Ensure the MRSProxy service is enabled on the on-premises Exchange Client Access servers.

3. Unified Messaging (UM) Mailboxes:

• Confirm that on-premises Skype for Business and Exchange Online meet UM requirements.

4. Licensing:

• Assign Office 365 licenses only after the migration completes. You have 30 days to assign licenses post-migration.

Permissions

• Assign the required administrative permissions to execute mailbox migrations. Review the "Mailbox Move and Migration Permissions" section in the Exchange documentation.

Step-by-Step Process for Migrating Mailboxes

Follow these steps to ensure a smooth migration:

1. Enable the MRSProxy Service

The MRSProxy service enables remote move migrations. If not enabled, follow these steps:

1. Open the Exchange Management Shell.

2. Run the following command to enable MRSProxy:

Set-WebServicesVirtualDirectory -Identity "Server\EWS (Default Web Site)" -MRSProxyEnabled $true

3. Verify the service status:

Get-WebServicesVirtualDirectory | Format-ListIdentity,MRSProxyEnabled

2. Create a Migration Endpoint

A migration endpoint establishes the connection between on-premises and Office 365 environments.

1. Navigate to Recipients > Migration > More > Migration Endpoints in the Exchange Admin Center (EAC).
2. Click New and provide the required details for your on-premises Exchange server.
3. Test the endpoint to confirm connectivity.

3. Configure the Migration Batch

Use the EAC or PowerShell to create and configure a migration batch:

• Using EAC:
  1. Go to Recipients > Migration > Add > Move to Exchange Online.
  2. Select the mailboxes to include in the batch.
  3. Specify batch options, such as notifications and scheduling.
• Using PowerShell:

New-MoveRequest -Identity <UserEmail> -RemoteTargetDatabase <DatabaseName> -TargetDeliveryDomain <Domain>

4. Monitor Migration Progress

Track the migration status using the EAC or PowerShell:

• EAC:
  • View the migration dashboard for real-time updates.
• PowerShell:

Get-MigrationBatch | Format-List Get-MigrationUserStatistics -Identity <UserEmail>

5. Remove Completed Batches

After migrations are complete, remove completed batches to prevent errors during future migrations:

• EAC:
  • Select the completed batch and click Delete.
• PowerShell:

Remove-MigrationBatch -Identity <BatchName>

Common Issues and Resolutions

1. Migration Endpoint Errors

• Cause: Incorrect configuration or connectivity issues.
• Solution:
  1. Verify the migration endpoint settings.
  2. Use the Microsoft Remote Connectivity Analyzer to test connections.

2. Stuck Migration Batches

• Cause: Network disruptions or large mailbox sizes.
• Solution:
  • Restart the batch:

Start-MigrationBatch -Identity <BatchName>

3. Missing Mailbox Data

• Cause: Incomplete synchronization.
• Solution:
  • Trigger a delta sync manually:

Sync-MigrationBatch -Identity <BatchName>

4. Permissions Errors

• Cause: Inadequate permissions assigned to the migration account.
• Solution:
  • Review and assign the necessary permissions.

Best Practices for Mailbox Migration

• Pre-Migration Checks: Verify all prerequisites before initiating migrations.
• Staggered Batches: Migrate mailboxes in smaller batches to reduce errors.
• User Communication: Notify users about the migration schedule and any potential impact.
• Post-Migration Validation: Confirm mailbox data integrity before marking migrations as complete.

Key PowerShell Commands for Migration Management

Command	Description
Set-WebServicesVirtualDirectory	Enable MRSProxy service.
New-MoveRequest	Create a new migration request.
Get-MigrationBatch	Check the status of a migration batch.
Sync-MigrationBatch	Perform a delta sync for a migration batch.
Remove-MigrationBatch	Delete a completed migration batch.

Conclusion

To Migrate mailboxes in a hybrid deployment requires meticulous planning and execution. By following the steps outlined in this guide, administrators can ensure a seamless migration with minimal disruptions. Addressing common issues proactively and adhering to best practices will further streamline the process.

Need help with mailbox migrations or configuring a hybrid deployment? Contact Medha Cloud today for expert guidance and support tailored to your business needs.

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• India: +91 93536 44646
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