Migrating large archive mailboxes from on-premises Exchange Server to Office 365 (Microsoft 365) can help to centralize data, improve accessibility, and reduce infrastructure overhead. Migration of large mailboxes requires careful planning as there might be size limits, performance constraints, and data inconsistencies. In this guide, we will explain the step-by-step process to migrate large archive mailboxes from a local Exchange Server to Office 365 using the hybrid model. We will also mention a specialized third-party Exchange migration tool that can simplify the migration of archive mailboxes from local Exchange Server to Office 365.
Stepwise Process to Migrate Archive Mailboxes to Office 365 (Microsoft 365)
Though there various native methods to migrate mailboxes from local Exchange to Office 365, the hybrid model is the ideal one when it comes to support, compliance, and ease of process. Let’s see the step-by-step process.
Step 1 – Prerequisites and Preparation Work
On the Exchange Online, you need to enable the archive for the users. This can be done with the below command.
Enable-Mailbox -Identity “[email protected]” -Archive
After this is complete, you need to enable the auto-expanding feature since you will be moving large archive mailboxes (which would be more than 50 GB and 100 GB in size). The auto-expanding feature is only applicable to the Exchange Online Plan 2 and Enterprise subscription. To enable this feature, use the below command:
Enable-Mailbox [email protected] -AutoExpandingArchive
You should consider the right license before attempting to migrate any data.
For the preparation of local mailboxes, it is best to do a health check on the mailboxes. The below script will check for large items which are over 150 MB and to confirm that there is sufficient free space for a stable move.
New-MailboxRepairRequest -Archive -Mailbox [email protected] -CorruptionType ProvisionedFolder,SearchFolder,AggregateCounts,FolderView
Step 2 – Create the Move Requests
The next step is to create the move request from the local Exchange Server to Office 365. You can use the New-MoveRequest command with the ArchiveOnly parameter to ensure that the items will be migrated to the online archive mailbox. Below is an example of the command:
New-MoveRequest -Identity “[email protected]” -Remote -RemoteHostName “mail.domain.com” -TargetDeliveryDomain “tenant.mail.onmicrosoft.com” -ArchiveOnly -BadItemLimit 2000 -LargeItemLimit 2000 -SuspendWhenReadyToComplete $true
This will create a new move request with the following parameters:
- RemoteHostName: It specifies the on-premises Exchange Server endpoint, which is the domain name.
- TargeDeliveryDomain: It is the Office 365 routing domain.
- BadItemLimit: This will allow 2000 bad items until the process is stopped.
- LargeItemsLimit: This will allow the migration to skip the oversized items.
Step 3 – Check the Status of Move Request
To check the status of the move request, you can use the below command in the Exchange Management Shell (EMS).
Get-MoveRequest -Identity “[email protected]” | Get-MoveRequestStatistics
Step 4 – Complete the Move
Once the status is finalized, the move will be in suspended state. You need to complete the move by using the below command:
Resume-MoveRequest -Identity “[email protected]”
Step 5 – Cleanup the Process
Once the migration is complete, the archive mailbox will be in the Exchange Online. The cleanup process is to remove the move requests which are marked as complete. This can be done using the below command:
Get-MoveRequest -MoveStatus Completed | Remove-MoveRequest
Things to Consider when Migrating Large Mailboxes to Office 365
There are a number of things that you should consider when migrating large mailboxes. Let’s explore the most common ones.
Throttling and Network Bandwidth
Large archive mailboxes might impact the data ingestion to Office 365. You should consider the local bandwidth that the company has, the network performance, and also the server’s storage performance. You should always consider migrating data in a maintenance window outside working hours and run the migration in batches.
There is also the impact from the Microsoft throttling polices. You should open a support request with Microsoft to relax such policies during the migration of data. This will reduce the migration time and timeouts.
Archive Mailbox Size Limit
In Office 365, the size of the online archive is set and defined, depending on the license purchased. If this is not taken into consideration, migrations will be paused and move requests would end up in Queued or StalledDueToTarget_ArchiveFull.
Bad Limit and Large Items Limit
Although there are no errors in the local archive mailboxes, you might encounter issues with either accumulated junk email or deleted items in the mailbox. This would cause bad items in the mailbox. Such items can be from a previous migration, restored from backup, or may contain legacy Outlook items. If this is the case and the pre-migration repair process was unsuccessful, you should consider a manual export and import process.
Similarly, large items could pause the migration or result in the move request failure.
A Quick and Easy Solution to Migrate Large Archive Mailboxes to Office 365
As you have seen, there are multiple steps involved when migrating large archive mailboxes from Exchange Server to Office 365 using the manual process. Moreover, you have to consider the mailbox size limit and other limitations on Office 365.
For quickly and easily migrating archive mailboxes to Office 365, you can use specialized Exchange migration tools, such as Stellar Migrator for Exchange. With this tool, you can easily and granularly migrate data from a local Exchange Server to Office 365 with no size limit. It offers features such as automatic source to destination matching, incremental (delta) migration to increase performance and bandwidth friendly seeding of data, and real-time/post-migration reporting. This helps reduce the complexities of migration and also reduce the point of failures and troubleshooting sessions.
Conclusion
Migration of large archive mailboxes will reduce the on-premises footprint, reduce the complexity of the setup, and also consolidate all the data. You should consider the best approach and solution to migrate archive mailboxes to Office 365. For a smoother migration of data with a peace of mind, you can use a specialized Exchange migration tool, such as Stellar Migrator for Exchange.
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