MicrosoftMicrosoft
MicrosoftInstall a single DC (let's say WS 2022) and make it a schema master. Install Exchange SE. Once all is done, you can remove that DC (after transferring the role to a WS 2025 DC). The fix for this should be out by end of calendar year when the problem will stop existing at all. My recommendation would be to NOT just run setup and open a ticket, because your AD replication might break. Exchange CU/Hu updates are not an issue; only the CU setup makes changes to schema.
There is no change to end of life for E2016/E2019, still less than a week away.
I'm in same situation with Domain Controllers already being Windows Server 2025 and was planning to upgrade Exchange 2019 CU14 to SE this weekend. Spun up a new Windows server 2022 like you mentioned and installed Active Directory. When promoting to a DC, I received this message. So is it possible to put a 2022 DC into a 2025 Environment?
The operation failed because:
The functional level of the forest is incompatible with this operating system.
"The version of the operating system is incompatible with the current AD DS forest functional level or AD LDS Configuration Set functional level. You must upgrade to a new version of the operating system before this server can become an AD DS Domain Controller or add an AD LDS Instance in this AD DS Forest or AD LDS Configuration Set."
This error can occur if you have not been granted necessary permissions to read data in the directory.
Any advice is appreciated!
Microsoft(Sorry I missed answering this before)
The issue here is that the FFL (Forest Functional Level) was already raised to Windows Server 2025. If that is done, then there is no going back / you cannot add DCs with older version of Windows Server OS. Documentation: How to raise Active Directory domain and forest functional levels - Windows Server | Microsoft Learn
The only fully safe way forward, in this case, is to wait until Windows team releases a fix for this, update your AD controllers and then move forward. The plan is to have it released by end of this year (not exactly sure if Nov. or Dec. but it should be very soon).
In related news: you should know that Exchange currently does not support Windows Server 2025 FFL. I'm not saying that you will have issues because of this (I did not hear of any) - but be aware: Exchange Server supportability matrix | Microsoft Learn
