Exchange Connectivity Count

We can use Get-counter cmdlet to get real-time performance counter data from local and remote computers:

Owa
Get-Counter “\MSExchange OWA\Current Unique Users” -ComputerName cas3

RPC
Get-Counter “\MSExchange RpcClientAccess\User Count” -ComputerName cas3

ActiveSync
Get-Counter “\MSExchange ActiveSync\Current Requests” -ComputerName cas3

Here is the similar thread for your reference:

https://social.technet.microsoft.com/Forums/office/en-US/aa693a3e-ddc2-48ed-998f-ba646bb11efa/exchange-2013-how-to-count-number-of-connection-to-server?forum=exchangesvradmin