Exchange 2013 CAS Error - TooManyOutstandingRequestsException: The number of outstanding requests for target mailbox server xxxxxxx has exceeded the limit value 5000

HI,

We are getting below error on Exchange 2013 CAS server for one of our mailbox server and ActiveSync user are unable get mails on mobile as well not able to send mails.

HttpProxyException=Microsoft.Exchange.HttpProxy.TooManyOutstandingRequestsException: The number of outstanding requests for target xxxxxxx has exceeded the limit value 5000  at Microsoft.Exchange.HttpProxy.ConcurrencyGuard.AddRequest(ProxyRequestHandler request)    at Microsoft.Exchange.HttpProxy.ProxyRequestHandler.BeginGetServerResponse()    at Microsoft.Exchange.HttpProxy.ProxyRequestHandler.<>c__DisplayClass38.<RequestStreamProxyCompleted>b__37();

Let me know if any one has faced such issue and how you resolve.

Thanks,

Manish