Lessen your client access server burden via throttling policies

Users can connect to Exchange Server 2010 using several different methods, which can overwork a client access server. Setting up client-throttling policies via the Exchange Management Shell will evenly distribute Exchange Server resources.

Users can connect to Exchange Server 2010 using a range of different connections that are all managed by a client access server -- Outlook, a POP3 client, ActiveSync, Outlook Anywhere, OWA and others. This can easily overload the CAS. Since Outlook and OWA are feature-rich and can put a strain on both the mailbox server's resources and Active Directory (AD), balancing the workload among multiple client access servers only partially solves the issue.

Implementing client-throttling policies prevents you from depriving your Exchange servers of resources. Client throttling policies ensure that users aren't overwhelming the system and that Exchange Server resources are proportionately shared among all sessions. Throttling policies are designed to stop users from consuming excessive amounts of server resources; they're not a substitute for proper capacity planning. This tip will introduce you to the various policies and their command syntax.

The default policy

When you install Exchange Server 2010 Enterprise Edition, Setup automatically implements a default throttling policy. You can modify this policy and create additional throttling policies. By doing so, you can define the acceptable load on a per-user basis.

Policy syntax

You can only configure throttling policies through the Exchange Management Shell. Let's take a look at the command syntax you'll use.

Throttling policies use Exchange Web Services parameters. Most of the time, three parts comprise these parameters: a component type, the phrase PercentTimeIn and a request type.

There are several different types of components you can address within a throttling policy. The key to throttling a component is knowing which acronym Microsoft associates with each component. Table 1 lists some important acronyms.

Table 1. Throttling policy component types and respective acronyms.


Component type


Exchange ActiveSync


Exchange Web Services/Unified Messaging


Outlook Web App






The PercentTimeIn portion of the Exchange Web Services parameter is simply a block of text that tells Exchange that you want to throttle access to a resource as a percentage of a minute. For example, setting this value to 50% indicates that you want the system to use the resource for 30 seconds.

The request type controls how much time the component can spend making requests of specific resources. You can control the amount of time a connection spends running code on the client access server, performing AD requests through LDAP and accessing mailbox resources via RPC requests. Table 2 lists the codes that Exchange uses to designate each request type.

Table 2. Here are the request types and their respective codes.


Request type


Client access server code


Active Directory (LDAP)


Mailbox requests (RPC)


The code for Outlook Web App is OWA and the code for the client access server is CAS. If you wanted to make sure that OWA clients don't overburden the client access server, use the OwaPercentTimeInCAS parameter.

If you wanted to prevent Unified Messaging clients from making excessive LDAP requests, you would use the EWSPercentTimeInAD parameter. This is because Unified Messaging falls under Exchange Web Services, which uses the code EWS and LDAP requests are associated with Active Directory, which uses the code AD.

About the author: Brien M. Posey, MCSE, is a six-time recipient of Microsoft's Most Valuable Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.

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