If you do not have a permanent connection to the Internet, then the user will need to dial directly into the VPOP3 computer or another computer on the network. This only works reliably if the dial-inserver is running Windows NT, Windows 2000 or later versions.

You need to install the Remote Access Server network service and configure this to allow incoming TCP/IP connections.

If the Remote Access Server is running on the VPOP3 computer itself, then you only need to allow inward access to the VPOP3 computer itself, otherwise you will need to allow inward access to the whole network.

You need to install the dial-in server portion of Windows 2000. Do this by going to Settings - Network and Dial-up connections - Make New Connection. Then choose Accept Incoming Connections and set it up appropriately.

If the Remote Access Server is running on the VPOP3 computer itself, then you only need to allow inward access to the VPOP3 computer itself, otherwise you need to allow access to the whole network. You set this on the Networking tab in the Internet Protocol Properties.