You receive a "server unavailable" error message when you try to connect to Exchange Server 2003 by using remote procedure call over HTTP

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When you try to connect to Microsoft Exchange Server 2003 by using a remote procedure call (RPC) over HTTP connection, you are unsuccessful, and you may receive an error message that is similar to the following:
Server unavailable
This issue may occur if you access the Internet behind a proxy server that requires outgoing authentication. When you access a Web site on the Internet and the proxy server requires outoing authentication, Internet Explorer prompts you for your credentials. Then, it proxies your request to the Web site. However, the RPC protocol that Microsoft Outlook uses does not contain a mechanism to inform the program that additional authentication is required. In this situation, the Microsoft Outlook program that uses RPC to try to connect to Exchange 2003 is not informed that it must use additional authentication to reach the Internet. Therefore, the RPC over HTTP connection is unsuccessful.
To work around this issue, turn off the authentication requirement for outgoing communications from your Outlook users.
More information
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
833401 How to configure RPC over HTTP in Exchange Server 2003
For additional information about how to configure Microsoft Office Outlook 2003 to connect to Exchange by using RPC over HTTP, visit the following Microsoft Web site:

Article ID: 822595 - Last Review: 12/08/2015 03:05:18 - Revision: 3.0

Microsoft Exchange Server 2003 Enterprise Edition, Microsoft Exchange Server 2003 Standard Edition

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