Topic Last Modified: 2008-02-07

This topic explains an issue that may cause Microsoft Office Outlook Web Access to return an error to users in two situations.

  1. In Outlook Web Access Premium, when you expand a folder that has one or more subfolders or click the Calendar, Contacts, or Tasks folder, you may receive the following error message: Microsoft Exchange issued an unexpected response (404).

  2. When you use Outlook Web Access to log on to a mailbox that is newly created, you may receive the error message HTTP Error 404 - File or directory not found after you configure the localization and time zone selection during the initial logon process.


These errors can occur when the .owa application extension mapping is missing in Internet Information Services (IIS) Manager.

Before You Begin

To perform the following procedure, the account you use must be delegated membership in the local Administrators group.

For more information about permissions, delegating roles, and the rights that are required to administer Microsoft Exchange Server 2007, see Permission Considerations.


To use IIS Manager to repair the .owa application extension mapping

  1. Log on to the Client Access server, and then open IIS Manager.

  2. Go to the /owa virtual directory under Web Sites/Default Web Site.

If you access Outlook Web Access through a Web site other than the Default Web Site, go to the other Web site.
  1. Right-click the /owa virtual directory, and then click Properties.

  2. On the Virtual Directory tab, click the Configuration button.

  3. Under Application extensions, look to determine whether .owa is included.

  4. If .owa is not included, click Add.

  5. To find the executable file, click the Browse button, and then browse to \Windows\Microsoft.NET\Framework\<latest version> and select aspnet_isapi.dll.

If the system is 64 bit, use \Windows\Microsoft.NET\Framework64\<latest version>\aspnet_isapi.dll.
  1. In the Extension field, enter owa.

  2. In the Verbs field, select Limit to, and then enter POST,GET.

  3. Make sure that the Script Engine check box is selected.

  4. Clear the Verify That File Exists check box.

  5. Click OK to save your changes.

  6. Click OK two more times to exit the /owa virtual directory properties.