Outlook Anywhere clients cannot connect to an Exchange server after you install Exchange Server 2010 SP3

Applies to: Exchange Server 2010 Service Pack 3


Assume that you install Microsoft Exchange 2010 Service Pack 3 (SP3) in an Exchange Server environment. There are many Outlook Anywhere (RPC over HTTP) clients in the environment. When the Outlook Anywhere clients try to connect to the Exchange server, the Outlook Anywhere clients are not connected. Additionally, the Outlook Anywhere clients receive the following error message:
503 Service Unavailable


This issue occurs because the limit of RPC over HTTP requests that ASP.NET can process is reached. 

The RPC over HTTP requests in Exchange Server 2010 SP3 rely on the ASP.NET runtime to process the requests. However, the default limit of ASP.NET requests is 25,000. 

Note In versions of Exchange Server earlier than Exchange Server 2010 SP3, RPC over HTTP requests do not rely on the ASP.NET runtime, and they are not affected by the request limit.


To resolve this issue, increase the limit of ASP.NET requests to the recommended value of 65535. To increase the limit of ASP.NET requests, follow these steps: 
  1. On the computer that is running the Client Access server role, locate the following file:
  2. Open the Machine.config file.
  3. In the <system.web> section, locate the following line:
    <processModel requestQueueLimit="25000" autoConfig="true" />
  4. Change the value of requestQueueLimit property to 65535.

More Information

You can use the following counters to monitor the number of ASP.NET requests and RPC over HTTP connections:
  • ASP.NET Apps v2.0.50727\_LM_W3SVC_x_ROOT_RPC\Requests Executing
  • RPC/HTTP Proxy\Current Number of Incoming RPC over HTTP Connections
When the issue occurs, the following errors are logged in the Internet Information Server (IIS) log:
2013-03-21 23:06:14 RPC_OUT_DATA /rpc/rpcproxy.dll cas.contoso.com:6001 443 CONTOSO\user MSRPC 503 3 0 15

2013-03-21 23:06:15 RPC_IN_DATA /rpc/rpcproxy.dll cas.contoso.com:6001 443 CONTOSO\user MSRPC 503 3 0 46