You use forms-based authentication on a server that is running Microsoft Exchange Server 2003 or Microsoft Exchange 2000 Server. When you try to log on to Microsoft Outlook Web Access, you cannot log on to the specified mailbox. Additionally, you receive the following error message:
HTTP/1.1 403 Forbidden
This problem occurs if the Exchange Server virtual directory inherits a Microsoft Internet Information Services (IIS) restriction that prevents ASP pages from loading. When this problem occurs, the Exchange server assumes that an ASP page is being loaded when the Exchange server receives the Outlook Web Access request. Therefore, the IIS restriction is applied.
For example, this problem occurs if you use the following e-mail address to log on to Outlook Web Access:
To work around this problem, use one of the following methods:
Add a secondary Simple Mail Transfer Protocol (SMTP) address to the affected user. The secondary SMTP address should have the following format:
Remove the IIS restriction that prevents ASP pages from loading.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.