You may receive multiple "HTTP 400 BadRequest" error messages from IIS when you configure Outlook 2003 to use RPC over HTTP to connect to an Exchange Server 2003 e-mail server

Consider the following scenario. You configure Microsoft Office Outlook 2003 to use a remote procedure call (RPC) over HTTP to connect to a Microsoft Exchange Server 2003 e-mail server. Microsoft Internet Information Services (IIS) 6.0 is running on the RPC proxy server. After every time that you connect to the e-mail server, you close Outlook 2003. In this scenario, you may receive multiple "HTTP 400 BadRequest" error messages from IIS.

In an environment that includes lots of users, you may receive an error message as frequently as every three to five seconds. Details for the "HTTP 400 BadRequest" error messages are logged in the Httperr.log file. This log file is located in the %windir%\System32\LogFiles folder on the RPC proxy server.

This behavior is by design.

The Http.sys component logs the "HTTP 400 BadRequest" error messages in the Httperr.log file because of the 1 gigabyte (GB) Content-Length HTTP header that the Rpcproxy.dll library uses. Rpcproxy.dll is the DLL that controls the extraction of RPC requests from the HTTP session. Rpcproxy.dll is an Internet Server API (ISAPI) that runs in IIS. The Rpcproxy.dll library listens for activity on the RPC virtual directory.

For more information about the Rpcproxy.dll library, visit the following Microsoft Web site: