Try these steps to follow to pinpoint the problem:
Unsurprisingly, Microsoft set the Premium version of OWA to be the default. The Basic version is available once you set up Forms Based Authentication at the Exchange 2003 server. Now this Basic version may look like an easy configuration but I found it tricky. However, that may be because Certificates are my Achilles heel.
From a theory point of view, you need a 3 part 'package', comprising of: Forms Based Authentication at the HTTP virtual server, IIS configured for SSL, and HTTPS (not http) in the browser. I say again, its the combination of IIS, SSL and certificates that I find the most difficult.
Forms Based AuthenticationOWA Exchange 2003
Forms Based Authentication means the users get a choice of Premium or Basic OWA 2003, and they have to supply their username, password and domain. Setting up Forms Based Authentication is simple; launch the Exchange System Manager, Server Icon, Protocols, and HTTP virtual server (Not SMTP). Right click, properties, and check the Forms Based Authentication tab.
Tip OWA 2003 Basic authentication logon with UPN Tip encourage users to logon with their UPN e.g. guyt@ cp.com
IIS, SSL and Certificates.
We are going to start with the assumption that you have Certificate Services installed on your domain.
Mission to Install the Certificate at IIS
From the IIS Snap-in (not the Exchange System Manager) expand the server name so that you see the Web sites. Right-click the Web site on which you want to install the certificate, and then click Properties. Click the Directory Security tab, and then select Server Certificate under Secure Communications. Now launch the Web Server Certificate Wizard and select: Create a new certificate. Now this certificate configuration section will either be a matter of following your nose and the certificate installs smoothly, or else it will be a whole separate project in getting these certificates up and running. If it's the latter, then take a time-out and seek extra advice on certificates.
Configuring IIS for SSLIIS Secure Communications for OWA - Require Secure Channel SSL
Navigate to IIS, select the Directory Security tab, the observe 3 options under Secure Communications. We need to set the Web site to require secure connections, click Edit and then Select Require Secure Channel (SSL). See diagram opposite.
We are ready to test SSL, here is a deliberate mistake, in your browser type http:// localhost/Postinfo.html. Did you you receive this error message? HTTP 403.4 - Forbidden: SSL required. What could be the problem? The answer is to start with httpS; so repeat but this time type: https:// localhost/Postinfo.htm
If you get a security alert 'The certificate is not from a trusted root CA'. Click Yes and a web page will appear - success.
OWA 2003 Browsers
Premium OWA 2003 requires IE 5.01 or later at the clients browser. Good news, OWA 2003 basic supports Mozilla Firefox and other non Internet Explorer browsers.
What you see at the browser when you connect depends on how the Exchange 2003 administrator sets the HTTP Virtual server. To get a choice of Premium (IE 5.01+) or Basic OWA, the Exchange 2003 administrator must configure Forms Based Authentication. The settings are on the Virtual HTTP server (not the Virtual SMTP.)
Note 1: In addition to OWA, you can connect the full Outlook 2003 to Exchange 2003 using RPC over HTTP. Previously, your users may have collected their email via a VPN. With this latest feature it's so much easier for roaming Outlook 2003 users to connect. See more about RPC over HTTP
Note 1: If you liked OWA, then investigate Remote Desktop Web Connection and get the XP experience in a browser.