Understanding Client Throttling Policies

Exchange Server 2010 uses client throttling policies to manage the performance of your Exchange organization. To do this, Exchange tracks the resources that each user consumes, and enforces connection bandwidth limits, as necessary

Exchange Server 2010 SP1, all client throttling policies are turned on by default. If you are experiencing problems that may be caused by these policies, you can turn off client throttling. To turn off client throttling, you can set all policy parameters to $Null

Exchange 2007 introduced a feature called RPC Client Throttling to allow administrators to manage end-user performance by preventing client applications, such as Outlook for example, from sending too many Remote Procedure Call [RPC] requests per second to Exchange, causing the server to suffer in terms of performance. When Exchange determines that a client is having a negative effect on the server, it will send a "back-off" request to the client telling it to delay sending any additional requests for a specified time (maximum of 2000 milliseconds) in order to reduce the performance effect on the server.

In Exchange 2010, Client Throttling has been much improved, monitoring and controlling much more than just RPC requests. Its purpose is still to ensure that users are not intentionally or unintentionally straining Exchange and that users share resources proportionally.

There is also Message Throttling in Exchange that restricts the number of messages and the number of connections that can be processed by an Exchange Transport server. In this article we will be talking only about Client Throttling.

What is Monitored?

what does Exchange 2010 now monitor that Exchange 2007 didn’t? As I mentioned before, with Exchange 2010 it's not just RPC requests that are monitored, but 9 different components:

* Anonymous access

* Cross-Premises Access (CPA)

* Exchange ActiveSync (EAS)

* Exchange Web Services (EWS)

* IMAP

* POP

* Outlook Web App (OWA)

* RPC Client Access (RCA)

* PowerShell

Below command shows a Default Throttling Policy created in Exchange 2010 SP1

     Get-ThrottlingPolicy      

Throttling Policies are simply AD objects saved under:

CN=Global Settings, CN=Exchange Org, CN=Microsoft Exchange, CN=Services, CN=Configuration, DC=Domain, DC=COM