Learn more about Exchange 2007 Client Throttling

I wanted to post a follow-up to Cathy's documentation announcement with a bit more information on RPC Client Throttling.

With the release of Microsoft Exchange Server 2007, a new feature known as RPC Client Throttling is available to administrators to help manage the end-user performance experience. RPC Client Throttling was introduced to help prevent client applications from sending too many RPC operations per second to the Exchange server which could decrease overall server performance. These client applications include desktop search engines searching through every object inside a user's mailbox, custom applications written to manipulate data that is located in Exchange mailboxes, enterprise-class e-mail archiving products, or CRM enabled mailboxes with e-mail auto-tagging enabled. Client throttling allows Exchange to identify and help prevent server monopolization by a few users. When a client is identified by the Exchange server as causing a disproportionate effect on the server, the server will send a "back-off" request to the client to reduce the performance effect on the server. To learn more about RPC Client Throttling, see Understanding Exchange 2007 Client Throttling.


- Tom Di Nardo

Comments (6)
  1. Diego Cogo says:

    I´m getting "Page Not Found" error for this link:


  2. JoeyM says:

    Hi Diego, this has been fixed – thanks for the heads up!

  3. Darryl says:

    The article refers to registry location "HKLMSystemServicesCurrentControlSetMSExchangeISParametersSystem".  On my mailbox role servers I have "HKLMsystemcurrentcontrolsetservicesmsexchangeisparametersSystem".  We’re talking about the same key?


    Nice feature.

  4. Mike Lagase says:


    You are correct, this is incorrectly stated. We’ll get that updated just as soon as we can.

    Thanks for pointing this out.

  5. jordi says:

    I’m thinking about an application accessing the mailbox server via Exchange web services. In that situation the Mapi connection to the mailbox is done by the CAS server in behalf of the application like this: application –(http)–> CAS –(Mapi)–> Mailbox.

    Is client throttling applied to server-to-server connections?

    For an application like Outlook there are two situations I can think of:

    – Using Mapi:

       Outlook –(Mapi)–> Mailbox

    – Using RPC over http:

       Outlook –(http)–> CAS –(Mapi)–> Mailbox

    Is client throttling applicable for Outlook clients using RPC over http?

  6. tdinardo says:

    Jordi – Thanks for your questions. Here are some answers:

    Is client throttling applied to server-to-server connections?

    No, client throttling only applies to MAPI clients.

    Is client throttling applicable for Outlook clients using RPC over http?

    Yes, client throttling is applicable to RPC/HTTP connections.

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