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You cannot connect to Microsoft Exchange through the Internet by using remote procedure call (RPC) over Hypertext Transfer Protocol (HTTP).
This problem occurs because Outlook does not correctly detect the settings in the Local Area Network (LAN) Settings dialog box when you connect to Microsoft Exchange through the Internet by using RPC over HTTP if both of the following conditions are true:
Caution Before changing any settings so that you can use HTTP to connect to your Microsoft Exchange Server mailbox, contact your Exchange server administrator.
To resolve this problem, specify both the proxy server and the port number in the Local Area Network (LAN) Settings dialog box in Microsoft Internet Explorer. To do this, follow these steps.
Note Contact your Exchange server administrator to obtain the information to complete these steps. For example, you must know the automatic configuration script and the correct name of your proxy server and port number.
In a local area network (LAN) environment, Microsoft Outlook communicates with the Microsoft Exchange server by using remote RPC with TCP/IP. This method provides quick, efficient access for a corporate network. However, in previous versions of both Exchange server and Outlook, access to an Exchange server by remote users required a virtual private network (VPN) connection to the corporate network. A VPN provides a remote user with a connection in an organization's corporate network and within its firewall. A VPN enables access to more network services than is required for just e-mail access.
For remote connections, Outlook now offers an alternative to VPN connections. Outlook can connect to an Exchange server through the Internet by using RPC over HTTP. This feature allows you to remotely access your Exchange server account from the Internet when you are working outside your organization’s firewall without any special connections or hardware, such as smart cards and security tokens.
There are several minimum requirements to use this feature. These include the following requirements: