Don’t use Windows Server 2025 DC as schema master FSMO role holder before installing Exchange

[psydii]

Oct 09, 2025
 

“do not use a Windows Server 2025 as your schema master FSMO role holder before installing an Exchange Server CU (including Exchange SE RTM)”

Note that SE RTM = Exchange 2019 CU15

 

“Windows Server 2025 schema master FSMO role holder might create duplicate schema attribute values after Exchange Server CU update is installed. After this happens, your AD replication might start failing”

 

“Environments where you might use Windows Server 2025 as domain controller with other roles are not impacted.”

“Windows Server team is working on a permanent fix for this issue (scheduled to be released in the following months).”

 

https://techcommunity.microsoft.com/blog/exchange/active-directory-schema-extension-issue-if-you-use-a-windows-server-2025-schema-/4460459

[DrCheese]

Server 2025 is a pretty big mess when it comes to running as a Domain Controller, with the Kerberos issues as well as this.

[psydii]

Yeah. They’ve got another four years to fix it though.  But unless they decide to move DC’s to the SE model they’re trying with exchange, I think there is a chance that AD might be gone in 2035.

[HPlum78]

Anyone else getting Windows Vista vibes from this OS?

[BOOT]

Yes. Both of them.

[mikes]

Should be  Do Not Use 2025 full stop.      MS usually fixed their buggy messes a year after release but doesn't seem the case with this !