In an earlier post, I explained how you can use Outlook Web Access (OWA) hosted on Exchange 2007 CAS Servers for accessing Exchange 2003 mailboxes in a co-existence environment by using the /exchange virtual directory.
Exchange Server 2007 CAS Servers come with Forms Based Authentication enabled by default. Now, if you wanted to disable the forms based authentication (required if you want to publish using ISA Sever 2006 Forms based authentication), OWA would still work fine internally (i.e. https://servername/exchange or /owa), as long as you choose Basic Authentication. The user will be presented with a popup password window instead of the form.
Now, what if you didn’t want users who are already logged in to the domain to be prompted for their password. The answer sounds simple – enable Integrated authentication, right?
Well, no. If you are co-existing Exchange 2003 and Exchange 2007 mailboxes and if your users have mailboxes on Exchange 2003 backend servers, and if they try to login via a CAS server using https://servername/exchange, they will receive an HTTP 404 Page not found message.
This is because ‘/exchange’ on the CAS is an Exchange 2003 virtual directory. Exchange 2007 supports Integrated Authentication only on Exchange 2007 virtual directories (see this article).
So the moral of the story is that you cannot enable Integrated Authentication on the CAS Server for the /exchange folder in an Exchange 2007 co-existence scenario. Exchange 2007 users can use Integrated authentication only if they use /owa virtual directory for accessing OWA.