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Cross-forest migration from Exchange 2013 to 2019/2016

Cross-forest migration refers to moving mailboxes, data, and other Exchange resources between separate Active Directory forests. This type of migration becomes necessary during events such as mergers, acquisitions, corporate restructuring, or business consolidations, where different IT environments must be unified. Combining Active Directory forests through migration helps centralize management, streamline resources, and boost collaboration across the organization.

Migrating mailboxes between different forests can be complex and time-intensive, particularly when using built-in tools. Native cross-forest migrations often require creating trust relationships between forests or running complicated PowerShell commands. Upgrading from older Exchange versions, such as Exchange 2010 or 2013, to newer versions like Exchange 2016 or 2019 can add further steps and increase complexity.

EdbMails Exchange Migration software offers a simplified and faster solution for cross-forest mailbox migration between on-premises Exchange servers. Its user-friendly, wizard-based interface automates much of the process, minimizing manual effort and reducing the risks associated with traditional migration methods.

Cross forest Exchange migration

EdbMails Exchange Migration tool makes it easy to migrate mailboxes, public folders, archive mailboxes, and shared mailboxes between different Active Directory forests, without facing coexistence challenges. You can directly migrate from Exchange 2010 or 2013 to newer versions like Exchange 2016 or 2019 with just a few clicks, making the migration process straightforward and stress-free.

The software is built for high-performance migration. It offers incremental migration, which means after the initial transfer, only newly added or changed items are moved, saving time and reducing server load. EdbMails also manages throttling automatically to avoid slowdowns and keep the servers stable during the migration process.

For organizations handling larger migrations, EdbMails supports transferring up to 20 mailboxes at the same time, speeding up the overall move. Advanced filtering options allow you to fine-tune what gets migrated — you can filter items by date range, sender, recipient, subject, attachments, or even message status (read/unread), ensuring only necessary data is transferred.

The upcoming sections will guide you through all essential prerequisites, detailed steps for cross-forest Exchange migration, and important post-migration tasks to complete a successful migration without disruptions.

Exchange cross forest migration prerequisites

Before you migrate to the target server, you need to create a valid mail-enabled user in the target forest with a specified set of Active Directory (AD) attributes. The following table illustrates the coexistence scenarios in various Exchange server versions.

Exchange server version	Coexistence scenario	Requirement	Migration
Exchange 2019	Possible. Can coexist with Exchange 2013 Can coexist with Exchange 2016	Exchange 2013 must have Cumulative Update 21 (CU21) or later Exchange 2016 must have Cumulative Update 11 (CU11) or later	EdbMails Exchange migration software allows you to migrate mailboxes to any Exchange server without worrying about coexistence requirements or limitations.
Exchange 2016	Can coexist with Exchange 2010 and Exchange 2013	Exchange 2010 must have the latest Rollup Update for Service Pack 3 (SP3)Exchange 2013 must have Cumulative Update 10 (CU10) or later

Step 1: Check that your system meets the Exchange server setup requirements.
The following links will help you set up your target Exchange server. Learn more about the network, hardware, coexistence scenarios, and operating system requirements for installing Exchange.
Step 2: Prepare your system with the following prerequisites for Exchange server
Complete the following prerequisites for Active Directory, Windows Mailbox server, and Windows Edge Transport servers before installing the target Exchange server.
Install cumulative updates (CU) on the source Exchange server
For migrating Exchange on-premises to Exchange, it is required that you have the latest cumulative updates (CU) installed on the source server.
1. Install for Exchange server 2016
2. Install for Exchange server 2019
Assign the Organization Management role group in Exchange to the admin user. It is an elevated permission that is required if you want to migrate Public folders.
Step 3: Set up the target Exchange server for migration
Given below is a list of key points for installing and preparing the Exchange server for migration.
1. Prepare AD and domains
  1. Before installing the Exchange server you need to prepare your Active Directory forest and its domains for the new version of Exchange.
  2. If you have a separate team to manage the Active Directory schema, you need to first extend the active directory schema, else proceed to the next step to prepare the Active Directory.
  3. If you have multiple domains you need to additionally prepare the Active Directory domains.
2. Install Exchange server on your computer
  Before installing the Exchange server, ensure that you meet the server system requirements and prerequisites as outlined previously. Next, follow the link to install Exchange 2016 or install Exchange 2019 from the setup wizard based on which server you want to migrate to.
3. Prepare a clean Exchange target environment
  1. Create and configure a send connector to send mail outside the Exchange organization.
  2. By default, Exchange automatically creates receive connectors for inbound mail flow when the mailbox server is installed. If you need to configure receive connectors, follow the steps in the link.
  3. Add accepted domains to allow recipients to send and receive email from another domain.
  4. Configure the default email address policy to add the accepted domain to every recipient in the organization.
  5. Configure external URLs (domains) on the virtual directories in the Client Access (frontend) services on the Mailbox server to allow clients to connect to your server from the internet (outside the organization’s network).
  6. Configure internal URLs on the virtual directories in the Client Access (frontend) services on the Mailbox server to allow clients to connect to your server from the internal network.
  7. Configure SSL certificates from a third-party certificate authority for services such as Outlook Anywhere and Exchange ActiveSync.
  8. Verify the Exchange server installation by running the command Get-ExchangeServer on the Exchange Management Shell (EMS).
4. Create trust relationship between forests (Optional)
  A forest trust is an authentication between two domains within the same Active Directory forest which creates a trust between two root domains for exchanging information. By creating a trust in advance, it is possible to address the trust issues during or after the migration.
5. Create mailboxes and Public folders on the Exchange server
  Before beginning the migration, ensure that mailboxes are available on the target Exchange server. You can opt to let EdbMails automatically create the mailboxes to simplify the process. If you prefer manual creation, please refer to the guidance provided in the links below.
  1. See how to create mailboxes in Exchange server
  2. Steps to create Public folder in Exchange server
6. Assign management roles to the admin account
  Set the following permissions to the admin account on the source and target Exchange server to migrate mailboxes on behalf of other users in your organization.
  - On the source server
    - ApplicationImpersonation
    - View-Only Configuration - Run the cmdlet New-ManagementRoleAssignment using the Exchange Management Shell to assign the View-Only Configuration role to the admin.
  - On the target server
    - Application Impersonation
    - View-Only Recipients
    - View-Only Configuration
7. Verify the mailbox of the admin account
  Check to see if the admin account that has been assigned management roles has a valid and non-hidden mailbox on the Exchange server.
8. Configure the throttling and message-size limits
  Create custom EWS throttling policies and configure message size limits on the Exchange server by following the steps in the links below.
  1. EWS throttling settings on Exchange server
  2. Configure message size limits on Exchange server
If you have deployed the Identity Lifecycle Manager (ILM) to synchronize the cross-forest global address list (GAL), ensure that you use the Microsoft Identity Manager 2016 SP1 and use the following code in the link to synchronize the source and target mailbox user.
If you have created the target mailbox user by using an Active Directory tool, run the Update-Recipient cmdlet to generate the LegacyExchangeDN. The following link outlines the procedure to create the target user by using PowerShell script.

Exchange cross forest migration step by step
- Step 1: Download and install EdbMails Exchange migration software
  - Download and install the EdbMails application on Windows operating system.
    See a detailed list of EdbMails system requirements for cross forest Exchange migration.
  - Launch the EdbMails application and either ‘login’ with your email address and password or select the ‘Start Your Free Trial’ option to continue.
  - Select ‘Live Exchange Migration’ option.
  - Select 'Live Exchange to Live Exchange Migration' option.
  - Keep the existing job name or select ‘New Job’ if you want to enter a different name.
- Step 2: Connect to the source Exchange server
  - To establish a new connection to the source Exchange server, click on ‘Add New Connection’. If you have an existing connection, simply select it from the list and click ‘Connect to Existing’ to continue.
  - Select the required connection options and click the ‘Next’ button.
    Different options to connect to Exchange server in EdbMails.
  - Enter the source Exchange server details and click the ‘Login’ button.
  - After logging into your source Exchange server, choose a method to load the mailboxes. EdbMails will automatically load them, but due to Microsoft API limitations, it may not display more than 100 mailboxes. If you have more than 100, you can use the ‘Load Mailboxes using .CSV file’ option to load them all.
- Step 3: Select the source Exchange mailboxes
  - Select the mailboxes/folders from the source Exchange server that you intend to transfer to the target server.
  - Click the ‘Next’ button.
- Step 4: connect to the target Exchange server
  - To establish a connection to the target Exchange server, click on ‘Add New Connection’ for a fresh connection. If you wish to use an existing connection, simply select it from the list and click ‘Connect to Existing’.
  - Choose the required options to connect to your target Exchange server and click the ‘Next’ button.
  - Enter the target Exchange server details , and then click the ‘Login’ button to proceed.
  - Select one of the methods to load the target Exchange server mailboxes.
- Step 5: Map the mailboxes between the source and the target servers
  - Select the required mapping option.
  - If EdbMails is installed on your target Exchange server, you can choose to let it automatically create the mailboxes on the target server.
    Learn more about automatic mailbox creation.
  - EdbMails automatically maps mailboxes between the source and target Exchange servers, making it especially helpful for migrating large numbers of mailboxes. This feature minimizes manual work.
- Step 6: Start Exchange cross-forest migration
  - After completing the mailbox mapping, click the ‘Start Migration’ button to initiate the migration process.
  - The cross-forest migration has now started. You can track the progress through the progress bar. Once the migration is finished, EdbMails will display a completion message. Click on the ‘View Logs’ button to check the migration report.
Exchange cross-forest post-migration tasks
- Step 1: Update the MX records to point to the new Exchange server
  To receive messages on the target Exchange server, update the MX records to route email to the new server. Additionally, configure the Autodiscover record so that Outlook can connect to the migrated mailboxes.
- Step 2: Create a new Outlook profile for users in the new domain
  Configure the Outlook profile for each user in your domain if Outlook has problems connecting to the new Exchange server.
- Step 3: Decommission and uninstall the source Exchange server
  After the migration to the target Exchange server is complete, decommission or uninstall the source server, depending on which Exchange server you used as the source.
  Steps to decommission Exchange server 2010
  Steps to decommission Exchange server 2013
Exchange cross domain migration troubleshooting
For assistance with migration errors, refer to the Exchange migration troubleshooting guide for a range of potential solutions. Additionally, for more insights into EdbMails Exchange migration, you may refer to the frequently asked questions (FAQs).

Benefits of EdbMails for Exchange cross forest migration

Support for all Exchange server versions: EdbMails supports seamless migration from Exchange 2003, 2007, 2010, and 2013 to both Exchange 2016 and 2019.
Cross-forest migration capabilities: The software effectively manages cross-forest domain migration without encountering coexistence issues.
Incremental migration: Incremental migration is designed to prevent the migration of duplicate items during subsequent operations.
Granular brick-level migration: With the granular brick-level migration feature, users can precisely select individual mailboxes and specific items for migration.
Public folders and Shared mailbox migration: EdbMails support for Exchange public folders and shared mailbox migration.
Support for all migration types: EdbMails Exchange migration software accommodates a variety of migration types, such as cutover, staged, and hybrid migrations.
User-friendly interface: EdbMails features an intuitive interface that simplifies the navigation process for performing migration operations, requiring no technical expertise.