How to Migrate from Microsoft 365 back to Exchange Server?

Exchange Server delivers data residency control by keeping data on local servers for staying compliant with laws such as GDPR. On top of that, it offers high availability via DAG, and Edge Transport Servers as an additional layer for spam filtering and protection. Due to these and other factors, many organizations migrate from Microsoft 365 back to on-premises Exchange Server.

In this article, we will discuss different paths you can take to migrate mailboxes back to Exchange Server. But first, we will discuss the reasons for choosing on-premises Exchange over cloud-based Microsoft 365.

Why Migrate from Microsoft 365 back to Exchange Server?

Exchange Server puts an organization in full control of their data and offers greater flexibility in enforcing security. Therefore, many organizations after moving to Microsoft 365 return to Exchange Server. Below are the main reasons influencing their decision:

Enhanced Security Controls and High Availability

On-premises Exchange Server setup provides full control to organizations over the data and security. For instance, they can add an Edge Transport Server to their Exchange environment to stop spam and viruses, and can deploy Data Availability Group (DAG) for high availability and site resilience. They can even set custom rules to block data leaks. 

Advanced Customization Options

Microsoft 365 doesn’t allow the same level of customization which is possible in on-premises Exchange Server. As Exchange Online PowerShell is mailbox/object-focused, it doesn’t provide server file system access. Moreover, Exchange admins cannot use custom transport agents built with .Net code. These transport agents are used for intercepting emails and performing actions such as modification, deletion, and redirection.

Cost Effectiveness 

As Microsoft 365 works on subscription-based model, the subscription cost may exceed the on-premises Exchange Server cost in the long-term, specifically for large organizations. If an organization already has the required hardware and a dedicated IT staff, then it may find on-premises server more cost-effective, depending on licensing, maintenance, security, and other requirements. 

Different Methods to Migrate from Microsoft 365 to Exchange Server

There are different ways to migrate from Microsoft 365 to Exchange Server. So, let’s explore these methods along with their advantages and disadvantages:

1. Hybrid Migration Method

You can use hybrid migration method for moving from Microsoft 365 to on-premises Exchange Server. Transferring mailboxes in this direction is officially called offboarding in Microsoft documentation. Follow the steps below to migrate from Microsoft 365 to Exchange using hybrid migration method:

1. Download Hybrid Configuration Wizard (HCW) using Microsoft Edge browser from the link https://aka.ms/HybridWizard (this link is provided by Microsoft).
2. Run the HCW to automate the creation of OAuth federation trust, provision certificates and create MRSProxy endpoint, which is required for offboarding from Microsoft 365 to Exchange Server.
3. HCW detects existing AD sync or prompts you for Entra ID installation/configuration during hybrid setup. 

1. After that, HCW configures inbound/outbound connectors. This enables Microsoft 365 to initiate remote move batches to your on-premises MRS.
2. You can use the commands in this Microsoft link to move mailboxes.
3. Mailboxes move in queues with incremental delta syncs. This is done while preserving all attributes such as X.500 addresses and permissions. 
4. After all the mailboxes are moved, update MX records to point to your on-premises Exchange Server’s public IP/FQDN, and modify SPF records to include your on-premises mail server. Inbound mails are then delivered directly to on-premises Exchange. 
5. Lastly, you should perform hybrid object cleanup using Exchange Admin Center (EAC) or Exchange Management Shell.

This method has the following advantages and disadvantages:

2. PST Export/Import Method

You can also export the mailboxes to PST using Microsoft Purview and then import them into Exchange Server. However, this method is suitable for small organizations. Follow the steps given below:

Note: Ensure that MX/SPF records are updated and pointing to on-premises Exchange Server. 

Step 1: Export PSTs using Microsoft Purview

• Open Microsoft Purview compliance portal and search for the mailboxes you want to export. For doing this, go to Content Search > New Search. After that, select target mailboxes and search.
• Once you have the content search results, export these results for selected mailboxes to PST format. It is to be noted that each PST file is capped at around 50 GB. If you are exporting a larger result set, it will automatically split into multiple PSTs.
• After export is complete, copy PSTs to a shared folder accessible by Exchange. Make a note of the UNC path of the network folder as you will need it while importing PSTs into Exchange. 

Step 2: Import PSTs into On-Premises Exchange 

• To import PST into on-premises Exchange, open Exchange Management Shell (EMS) and run the command – New-MailboxImportRequest -Mailbox <User> -FilePath “\Server\Share\user.pst”. This will import PST into the specified mailbox on on-premises Exchange Server.
• To monitor progress of mailbox import, you can use the Get-MailboxImportRequestStatistics -Identity <RequestId> command.
• After successful PST import, clean up the requests by using the Complete-MailboxImportRequest -Identity <RequestId> command. 

This method has the following advantages and disadvantages:

An Easy Solution to Migrate Data from Microsoft 365 to Exchange Server

You can use specialized Exchange migration tool to directly migrate mailboxes from Microsoft 365 to Exchange Server. Apart from user mailboxes, this tool also migrates archives and public folders with 100% precision. While transferring mailbox data, the tool maintains data integrity and preserves folder structure. 

This Exchange migration tool has an auto-mailbox matching feature to map mailboxes automatically using mailbox ID. It provides delta (incremental) migration feature that allows you to migrate only the new items received after the initial migration or the items, which are not migrated during the previous attempt. As a result, it reduces administrative effort and consumption of Exchange resources. In addition, this tool supports local Exchange to local Exchange migration, local Exchange to Microsoft 365 migration, and Microsoft 365 to Microsoft 365 migration.

Conclusion

There are varied reasons why organizations migrate from Microsoft 365 back to on-premises Exchange Server. Above, we have discussed different ways to migrate from cloud to local Exchange. For direct and seamless data migration, you can use a specialized Exchange migration tool, such as Stellar Migrator for Exchange. It doesn’t require you to run complex PowerShell scripts and securely migrates mailboxes with 100% precision. It supports cross-forest, same-domain, and cross-domain migrations without any need for establishing a trust relationship between Active Directory forests.