By default, you have to use PerfMon counters to see how often throttling is occurring for RPC connections.
However, there is a way to have this information properly logged. To achieve this, modify the Microsoft.Exchange.RpcClientAccess.Service.exe.config file located in \Program File\Microsoft\Exchange Server\V14\Bin and add Throttling to the LoggingTag string so it looks like this:
<add key=”LoggingTag” value=”ConnectDisconnect, Logon, Failures, ApplicationData, Warnings, Throttling”/>
Now restart the RPC Client Access service and you will see this information in logs created in the “\Program Files\Microsoft\Exchange Server\V14\Logging\RPC Client Access” folder. When throttling happens, you will usually find the keyword “exceeded”.
This way, you can easily see when RPC Throttling kicks in, what it is doing and why!