Cross Forest Migration of Exchange and Office 365 Mailboxes – An Easy Method

Summary: Cross Forest migration is a tedious task that requires you to use command-line tools, such as EMS and PowerShell scripts that are time-consuming and may result in errors leading to data loss. In this guide, we’ve discussed cross forest mailbox migration and steps to easily migrate Exchange mailboxes from one forest to another using third-party software, such as Stellar Converter for EDB, with 100% integrity and consistency.

Cross Forest Migration of Exchange and Office 365 Mailboxes – An Easy Method

Cross Forest or Cross-Domain migration is a process of migrating Exchange mailboxes from one Active Directory forest to another. A Cross Forest migration is often needed when there is a new MS Exchange deployment with a new domain name, and you need to migrate the mailboxes from the current domain or legacy version.

Cross Forest Migration

Further, factors, like company mergers, acquisitions, name change, and segmentation of the IT environment due to security reasons also require the organization to perform a cross forest migration.  

However, Cross Forest migration is a tedious, complex, and time-consuming task. It requires the right expertise and technical knowledge to perform the migration.

Microsoft provides tools, such as Active Directory Migration Tool and PowerShell scripts (such as Prepare-MoveRequest.ps1 located in C:\Program Files\Microsoft\Exchange Server\V15\Scripts\ folder) to perform cross forest migration. However, you need to perform multiple manual steps, which may lead to errors causing extended downtime. This can significantly affect the business and impact users’ productivity.

Further, if you are required to migrate from a legacy version (Exchange 2010 or earlier version) to Exchange 2016 or 2019, you need to perform the migration in two steps.

Thus, many organizations prefer to use a third-party tool, such as Stellar Converter for EDB, to migrate user mailboxes across the forests.

Although third-party software comes with a price tag, you don’t need to perform complex tasks, run PowerShell scripts, or use PowerShell cmdlets to perform a cross forest mailbox migration. Also, you don’t need to create or map user mailboxes on the destination server manually. The software automatically maps the source and destination mailboxes.

With the help of the software, you can migrate mailboxes from your current forest or legacy Exchange server version directly to Exchange 2013, 2016, 2019, or Office 365.

It automates and simplifies the entire cross forest mailbox migration process and helps you quickly migrate the user mailboxes from one forest to another in a few clicks.

Steps to Migrate Mailboxes from One Forest to Another

Below we have discussed the steps to migrate mailboxes from existing forest (domain server) to a new forest using Stellar Converter for EDB. You can download the free demo version to evaluate the software before activation.

The demo version lets you scan and preview mailboxes and mail items from the Exchange database (EDB) file. You must activate the software to export or migrate the mailboxes to the Exchange server on the new forest. The detailed steps are as follows:

Step 1: Scan Exchange Database File

To migrate the mailboxes directly to Office 365 or live Exchange server on another forest, you need to dismount the Exchange database file on the current forest server. Also, configure the destination server’s administrator profile in Outlook. Then follow these steps:

  • Install and launch Stellar Converter for EDB software. In the ‘Select File’ dialog box, click ‘Browse’ to choose the offline EDB file. Also, select the ‘Temp path’ or keep it default and then click ‘Next.
Select EDB File
  • After the scan, the software displays a three-pane preview window where you can click on the mailbox items to see their preview.
Preview Mailboxes
  • You can also search mailboxes and emails that you want to migrate to another forest and filter your search using parameters, such as To, From, Subject, Date, etc.
Select Mailboxes
  • After selecting the mailboxes, click ‘Save Converted File’ under the ‘Home’ menu. This will display a ‘Save As’ dialog box with multiple saving options.

Step 2: Export Mailboxes to Live Exchange Server

To export the mailboxes to the live Exchange server on another forest, follow these steps:

  • In the ‘Save As’ dialog box, choose ‘Export to Live Exchange’ and click ‘Next.’
Export to Exchange
  • In the ‘Enter Login Credentials’ dialog box, choose ‘Profile Name’ (that you configured in Outlook) and enter the password. Also, enter the ADS name, Admin mailbox email, and password. Then click ‘Next.’
Enter Exchange Credentials
  • In the Map Mailboxes window, the software automatically maps the source and destination mailboxes. However, you can also click ‘Create Mailbox’ to manually create and map mailboxes on the destination server.
  • Further, you can set priority to prioritize export of important mailboxes first than others. The ‘Apply Filter’ button allows you to exclude or include mailboxes based on the email address and date range.
Map Users Mailboxes
  • Once mailbox mapping is done, click ‘Export’ to migrate the mailboxes.
Exporting Mailboxes

Step 3: Export Mailboxes to Office 365

To migrate mailboxes to Office 365 directly, follow these steps:

  • After scan and preview, from the ‘Save As’ dialog box, choose ‘Export to Office 365’ and click ‘Next.’  
Export to Office 365
  • Choose the configured Outlook profile with admin privileges and enter the password. Click ‘OK’ to proceed.
Enter Credentials Office365
  • The software auto-maps the mailboxes. However, you can set the mailbox priority order or edit the mailbox mapping manually. Further, ‘Apply Filter’ allows you to include/exclude mailboxes based on the email address and date range.
Map Mailboxes
  • After mapping, click ‘Export.’ This will start exporting or migrating the mailboxes from one forest to another.
Export Mailboxes

The software uses the Parallel Processing technology that helps process and migrate mailboxes from source to destination server at 4x speed. It exports up to 4 mailboxes simultaneously, which significantly reduces the migration time and effort.

After Cross Forest mailbox migration, you can redirect users to the mailboxes in the new forest.


Cross Forest migration is easier with the help of Stellar Converter for EDB. It helps small, medium, and large enterprises migrate their mailboxes quickly to another Exchange forest or domain with 100% precision, integrity, and accuracy. Manual methods are complex, time-consuming, and can also lead to errors and data loss situations.

Thus, it’s recommended to use Stellar Converter for EDB to avoid errors and ensure smooth cross forest mailbox migration to a live Exchange server or Office 365 at 4x faster speed. For more help or any queries, leave a comment.

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