Domain Upgrade from 2012R2 to 2019 Exchange Compatibility

Question

According to Microsoft, Exchange 2013 (highest CU) isn't compatible with a domain controller level of 2019. At least if I'm reading this matrix correctly:

https://docs.microsoft.com/en-us/Exchange/plan-and-deploy/supportability-matrix?redirectedfrom=MSDN&view=exchserver-2019

With a 2012R2 domain currently, if I build a 2019 server and promote it to domain controller. Will this cause issues immediately or only if the domain/forest functional levels are upped?

I wouldn't immediately raise the domain/forest functional levels. If this works, I would be on 2012R2 domain/forest functional with 2019 domain controllers in the hybrid domain setup, until our Exchange environment is migrated and then we can up our domain/forest functional levels.

I'm thinking I will have to either migrate Exchange 2013 to either 2019/Exchange Online first, then we can build our new domain controllers and continue the migration.

Answer 1

If you don't need any features/functions that Windows Server 2019 brings, then leave your Domain Controllers as is until you complete your migration. Once the migration is complete you'll need to determine how you're going to manage Exchange attributes for your on premises objects synced to Office 365 and take appropriate steps. (ADSIEdit, Exchange Server 2019, or this https://practical365.com/removing-the-last-exchange-server and this https://docs.microsoft.com/en-gb/Exchange/manage-hybrid-exchange-recipients-with-management-tools).