Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1
Topic Last Modified: 2009-04-10

This topic explains how to configure Microsoft Exchange Server 2007 Client Access servers to enable more than 5,000 concurrent Exchange ActiveSync connections. The Airsync feature requires an open connection for each user. When the number of concurrent connections reaches the limit that is set in the requestQueueLimit parameter in the Machine.config file, users receive error messages on their ActiveSync devices that resemble the following:  

OPTIONS /Microsoft-Server-ActiveSync

Content-Type: application/

MS-ASProtocolVersion: 12.0

HTTP/1.1 503 Service Unavailable

Connection: close

Date: Date Time

Server: Microsoft-IIS/6.0

X-Powered-By: ASP.NET

Content-Type: text/html

Options command success! Total time: 0 ms, Transmis

By default, the requestQueueLimit parameter is set by ASP.NET to 5000. To have more than 5,000 concurrent Exchange ActiveSync connections, you must change the requestQueueLimit parameter in the Machine.config file. The requestQueueLimit parameter can be set up to 9000. 

To change the requestQueueLimit parameter
  1. On the computer that is running the Client Access server role, start Windows Explorer.

  2. Locate the following file:


  3. Open the Machine.config file.

  4. In the <system.web> section, locate the following line:

    <processModel requestQueueLimit="5000" autoConfig="true" />

  5. Change "5000" in this line to the number of concurrent connections that you want to enable, save the file, and then close it.

The requestQueueLimit parameter is a global parameter. Changes to this parameter affect all application pools.
Microsoft .NET Framework version 3.5 Service Pack 1 (SP1) includes an update that lets you use the Aspnet.config file to configure the number of concurrent Exchange ActiveSync connections. The setting in the Aspnet.config file overwrites the setting in the Machine.config file.