You can use an Outlook Web Access (OWA) URL that you establish in Exchange Server 5.x in Exchange 2000 Server, even though OWA in Exchange 2000 is substantially different from OWA in Exchange Server 5.5. Exchange 2000 no longer uses Active Server Pages (ASP) pages for client access or the Messaging API (MAPI) to access the user's mailbox. This architecture proved difficult to scale, and reliance on MAPI-based access to the mailbox limited the effective number of users who could simultaneously use OWA.
Instead, Exchange 2000 uses the Web Store as the mechanism to access mailbox and public folder data. The Web Store is compiled or binary, and because you don't have access to the source code, it's more difficult to manipulate.
Because Exchange 2000 doesn't use ASP, your customized ASP logon and logoff screens won't migrate; OWA 2000 doesn't use these introduction or banner screens. If OWA users have logged on to the domain, they don't have to enter their email alias. When a user requests the OWA URL, the Exchange 2000 server takes the information about the user's mailbox from Active Directory (AD). Users accessing OWA from the Internet must provide their domain credentials. The session receives the information about their mailbox through AD and opens OWA.
OWA in Exchange 2000 looks more like Outlook 2000 than earlier versions did; for example, both new versions support calendar and contact information in public folders. However, OWA still has limitations (e.g., no support for Global Address List—GAL, rules).
Exchange 2000 uses Microsoft IIS 5.0, which you install automatically when you install Exchange 2000. This feature shows the integral relationship between Exchange's Web Store and IIS.
The good news is that the methods I present in this article still work with Exchange 2000. However, of the two methods, Method 2 scales best for Exchange 2000 because you need only relocate the IP address associated with the URL to your Exchange 2000 server and reapply the redirection procedure.
In multiserver environments, Exchange 2000 introduces front-end/back-end server architecture. Using Method 2, you can assign one URL and IP address to a front-end server. The front-end server accepts the request, references the user credentials in AD, and passes the credentials to the appropriate Exchange back-end server.