In an environment where one DC exist after adding Windows 2012 R2 Servers as additional servers, Exchange 2007 doesn’t show the new servers although they also hold GC.
To locate the problem you should search the event ID (2080) which shows the populated DCs and the permissions allowed on Exchange servers
In the below screenshot, the SACL right was not provided to the new DCs due to GPO problem.
After checking sites, Replication, all is healthy and no issue with it.
3 servers (Two 2012 servers) and one DC 2003 Server
Exchange 2010 SP3 servers.
The Default Domain Controllers Policy was not linked to the Domain Controllers OU.
After Linking the Domain Controllers OU to the Default Controllers policy, the SACL permission was provided without any issue.
Now Exchange is reporting healthy and can read the new DCs which allow us to demote the old DCs
After removing the old DC
Hope you find this useful