When you try to start Microsoft Exchange services, the services don't start, and the following event is logged in the Application log:
Log Name: Application
Date: 3/18/2016 4:15:00 PM
Event ID: 2142
Task Category: Topology
Process Microsoft.Exchange.Directory.TopologyService.exe (PID=1376) Forest contoso.com. Topology discovery failed, error details
No Minimal Required Number of Suitable Directory Servers Found in Forest contoso.com Site Default-First-Site-Name and connected Sites..
This issue may occur if the total number of available domain controllers across multiple Active Directory sites is less than the MinSuitableServer value (the default value is 3).
To resolve this issue, restore the number of available domain controllers to a number equal to or greater than the MinSuitableServer value.
Article ID: 3090811 - Last Review: 28 Sep 2016 - Revision: 1