Exchange Server SE on Windows Server 2025: supported platforms, coexistence and planning

Exchange Server 2016 and 2019 reached end of support on 14 October 2025, so every on-premises organization should now be on Exchange Server Subscription Edition (SE). Many teams combine that move with a refresh onto Windows Server 2025. Before you order hardware, check exactly what Microsoft supports: Windows Server versions, domain controllers, .NET Framework, Outlook clients, which Exchange versions can coexist, and the one upgrade shortcut that isn't allowed.

The support picture at a glance#

Condensed from the Exchange SE column of Microsoft's supportability matrix:

Exchange 2019 has the same Windows Server list. Exchange 2016 ran only on Windows Server 2016, 2012 R2 and 2012, and its row in the matrix doesn't include Windows Server 2025 domain controllers. That's one more reason to finish removing it.

Coexistence and upgrade paths#

• Exchange 2013: Exchange SE RTM setup won't install into an organization that still has Exchange 2013 servers.
• Exchange 2019 CU14 or CU15: can be upgraded in place to SE, much like installing a cumulative update (see in-place upgrade from Exchange 2019 to SE).
• Exchange 2016: no in-place path. Add SE servers, move everything across, then uninstall the 2016 servers (Microsoft calls this a legacy upgrade).
• Exchange SE CU2: its setup will refuse to coexist with versions that are unsupported when it ships. SE follows the Modern Lifecycle Policy and is supported only while you stay current, so staying on an older CU to avoid that block isn't a long-term option.
• Windows Server: upgrading the operating system in place between major versions (for example Windows Server 2022 to 2025) with Exchange installed isn't supported. Microsoft lists new hardware and a newer Windows Server version among the reasons you need a legacy upgrade.

In practice, to get Exchange SE onto Windows Server 2025 you build new servers and move to them, even if your current servers already run SE.

Step by step: planning the move to Windows Server 2025#

1. Inventory what you run today#

Get-ExchangeServer | Format-Table Name, Edition, AdminDisplayVersion -AutoSize

Invoke-Command -ComputerName EX01, EX02 -ScriptBlock {
  [pscustomobject]@{
    OS         = (Get-CimInstance Win32_OperatingSystem).Caption
    NetRelease = (Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full').Release
  }
} | Format-Table PSComputerName, OS, NetRelease -AutoSize

Get-ADForest | Format-List ForestMode, SchemaMaster
Get-ADDomainController -Filter * | Format-Table Name, OperatingSystem, IsReadOnly, Site -AutoSize

A .NET Release value of 533320 or higher is 4.8.1; 528040 or higher is 4.8. The Exchange Health Checker also reports each server's operating system and .NET version and flags unsupported combinations.

2. Get Active Directory ready#

• Every Active Directory site that contains Exchange servers needs writable domain controllers and global catalogs. Windows Server 2025 DCs are fine; support for them arrived with Exchange 2019 CU14.
• If a Windows Server 2025 DC holds the schema master role, install the November 2025 or later cumulative update on it before you run any PrepareAD operation. Microsoft requires this to avoid Active Directory replication issues.
• Windows Server 2025 introduced a new forest functional level, but the matrix lists only Windows Server 2016 and 2012 R2 for Exchange. Don't raise the forest level until Microsoft lists the new one.

3. Build the new servers#

Install Windows Server 2025 (Server Core if your backup, antivirus and monitoring agents support it), then the prerequisites from Microsoft's Exchange SE system requirements. Setup's readiness checks enforce them. Install from the latest SE media (so far that's the RTM build, because no SE CU has shipped yet), then the latest security update:

D:\Setup.exe /Mode:Install /Roles:Mailbox /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF

Straight after setup, set the new server's Autodiscover SCP and virtual directory URLs to your namespace. If you don't, Outlook may meet its default server name (see fixing the "name on the security certificate is invalid" alert).

4. Create a new DAG and move into it#

A DAG runs on Windows failover clustering, and Microsoft requires all DAG members to run the same operating system. The Windows Server 2025 servers therefore form a new DAG; you don't add them to the old one. Then move, in this order:

1. Certificates (import your SAN certificate and enable it for IIS and SMTP) and load balancer pools.
2. Mailboxes, plus arbitration, audit log and public folder mailboxes (see missing arbitration mailboxes for what breaks if you forget them).
3. Send connector source servers, relay receive connectors, backup jobs and monitoring.
4. Uninstall the old servers with Exchange setup.

Verify#

Get-ExchangeServer | Format-Table Name, AdminDisplayVersion -AutoSize
Get-DatabaseAvailabilityGroup -Status | Format-List Name, Servers, OperationalServers
Get-MailboxDatabaseCopyStatus * | Format-Table Name, Status, CopyQueueLength, ContentIndexState -AutoSize

Good looks like this: every server on the same, current SE build; all new members listed under OperationalServers; copies Mounted or Healthy with low queues and healthy content indexes; and a Health Checker report with no operating system, .NET or Active Directory warnings.

Tips and gotchas#

• Clients: Outlook 2016 and 2019 are still in the matrix, but Office 2016 and 2019 are out of support themselves, so plan Microsoft 365 Apps or Outlook 2024. The new Outlook for Windows isn't in Microsoft's list for Exchange Server.
• OWA Light: according to the matrix, it's disabled starting with the August 2026 security update.
• Windows Server 2019 is already in extended support, so new builds should go to 2025 (or 2022) rather than 2019.
• Licensing: Microsoft has said a later SE cumulative update brings a new product key requirement. Read each CU's release notes; the licensing side is covered in Exchange Server SE explained.

References#

• Exchange Server supportability matrix (Microsoft Learn)
• Upgrading to Exchange Server Subscription Edition (SE) (Microsoft Learn)
• Plan for high availability and site resilience (Microsoft Learn)