Upgrading from Microsoft Exchange Server 2019 to Exchange Server Subscription Edition (SE) in a Database Availability Group (DAG) environment requires careful planning, validation, and staged execution. This guide walks through a rolling upgrade process designed to minimize downtime while maintaining mailbox database availability throughout the transition.
Upgrade Goal
The objective of this upgrade is to move an existing Exchange Server 2019 DAG deployment to Exchange Server Subscription Edition using an in-place rolling upgrade model. Each DAG member is upgraded individually to preserve service availability and mailbox resiliency during the process.
This article is part of the Infrastructure & Systems Guide cluster, where RavenHawkTech organizes practical systems administration, lifecycle management, monitoring, recovery, and enterprise operations guidance.
Why This Matters
Exchange Server Subscription Edition introduces Microsoft’s modern servicing model for on-premises Exchange environments. Organizations upgrading from Exchange 2019 benefit from continued support, security updates, and long-term platform viability. In DAG environments, following a structured rolling upgrade approach is critical to avoid mailbox database outages or replication failures.
Recommended Prerequisites
- Exchange Version: Exchange Server 2019 CU14 or later
- Operating System: Windows Server 2019 or Windows Server 2022
- Backups: Full Exchange server and mailbox database backups completed
- DAG Health: Replication and mailbox database status verified
- Patching: All Exchange servers fully updated
- Maintenance Window: Scheduled rolling upgrade plan for each DAG member
Step 1: Prepare Active Directory
Before upgrading any Exchange servers, extend the Active Directory schema and prepare the Exchange organization using the latest Exchange SE installation media.
Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms_DiagnosticDataON Setup.exe /PrepareAD /OrganizationName:"YourOrg" /IAcceptExchangeServerLicenseTerms_DiagnosticDataON Setup.exe /PrepareAllDomains /IAcceptExchangeServerLicenseTerms_DiagnosticDataON
Tip: Run the schema preparation commands directly from the Active Directory Schema Master to avoid replication inconsistencies during the upgrade process.
Step 2: Validate DAG Health
Validate the health of the DAG and mailbox database replication before placing any Exchange server into maintenance mode.
Get-DatabaseAvailabilityGroup -Status Test-ReplicationHealth Get-MailboxDatabaseCopyStatus *
Step 3: Place the DAG Member Into Maintenance Mode
Move active mailbox databases away from the target server and suspend cluster participation before starting the Exchange SE upgrade.
Set-ServerComponentState <ServerName> -Component ServerWideOffline -State Inactive -Requester Maintenance Suspend-ClusterNode <ServerName> Set-MailboxServer <ServerName> -DatabaseCopyAutoActivationPolicy Blocked Move-ActiveMailboxDatabase -Server <ServerName>
Warning: Never upgrade all DAG members simultaneously. Maintain at least one healthy Exchange DAG member online and capable of hosting active mailbox databases throughout the migration window.
Step 4: Perform the Exchange SE Upgrade
Mount the Exchange Server Subscription Edition ISO and run the in-place upgrade command on the DAG member currently in maintenance mode.
Setup.exe /Mode:Upgrade /IAcceptExchangeServerLicenseTerms_DiagnosticDataON
After the installation completes, reboot the Exchange server and validate that all Exchange services initialize successfully before continuing.
Step 5: Bring the Server Back Online
Once the upgraded server passes validation checks, return it to active DAG participation and redistribute mailbox databases.
Set-ServerComponentState <ServerName> -Component ServerWideOffline -State Active -Requester Maintenance Resume-ClusterNode <ServerName> Set-MailboxServer <ServerName> -DatabaseCopyAutoActivationPolicy Unrestricted RedistributeActiveDatabases.ps1 -DagName <DAGName>
Step 6: Perform Post-Upgrade Validation
- Mail Flow: Verify inbound and outbound email delivery
- OWA and ECP: Confirm administrative and user access
- Database Health: Validate replication status across DAG members
- Transport Queues: Review queue health using Get-Queue
- Exchange Version: Confirm all upgraded servers report Exchange SE
Get-Queue Get-ExchangeServer | ft Name,Edition,AdminDisplayVersion
Important Operational Considerations
- Temporarily disable or bypass antivirus and EDR tooling during the Exchange upgrade process when operationally approved.
- Verify Exchange certificates after each server upgrade.
- Monitor Windows Event Logs and Exchange health throughout the migration.
- Keep the mixed Exchange 2019 and Exchange SE coexistence period as short as possible.
Best Practice: Upgrade and validate one DAG member at a time before proceeding to the next server. This significantly reduces operational risk and simplifies troubleshooting if unexpected replication or transport issues occur.
Related Infrastructure Reading
- Infrastructure & Systems Guide — the main RavenHawkTech hub for systems administration, monitoring, lifecycle management, and operational reliability.
- Troubleshooting & Recovery Guide — incident handling, recovery planning, and practical troubleshooting workflows.
- Top 10 IT Mistakes That Cause Outages — operational issues that commonly lead to service disruption.
Final Thoughts
Exchange Server Subscription Edition upgrades in DAG environments are straightforward when approached methodically. Careful validation, maintenance mode handling, and staged rollouts ensure that mailbox availability remains protected while transitioning to Microsoft’s supported Exchange platform for the future.