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Open Windows Firewall by clicking the Start button
, clicking Control Panel, clicking Security, and then clicking Windows Firewall. -
Click Allow a program through Windows Firewall.
If you are prompted for an administrator password or confirmation, type the password or provide confirmation. -
Click Add port.
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In the Name box, type a name that will help you remember what the port is used for (Alternative SMTP)
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In the Port number box, type the port number 26
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Click TCP or UDP, depending on the protocol.
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To change scope for the port, click Change scope, and then click the option that you want to use. ("Scope" refers to the set of computers that can use this port opening.)
Reference: http://windows.microsoft.com/en-us/windows-vista/open-a-port-in-windows-firewall
