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I recently installed Exchange Server 2003 Service Pack 1 (SP1). The installation went smoothly, but Outlook Web Access (OWA) began refusing logons from nondomain browsers and allowing access from domain browsers. During SP1 installation, a check box in the IIS properties of the Web site on which OWA is installed had reset, enabling Integrated Windows Authentication. This setting is used mostly on Intranet Web sites on which the currently logged on user's username and password are passed to Integrated Windows Authentication for authentication. On a public resource such as OWA, Integrated Windows Authentication is unnecessary and can make OWA and many browsers inaccessible if the setting is enabled. After I cleared the Integrated Windows Authentication check box, OWA resumed working.