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→Testing the connection to the Postfix Service
::'''NOTE:''' If it worked, this indicates that the postfix service is running, listening, and responding to connections.
<ol><li value="4">Let's see if it works from other machines. Use '''nc''' to connect to '''vm2''' from '''vm3''' and see if it works. If your firewall is set up properly, the nc command should not permit a connection (i.e. '''no route to host''').</li>
<li>Create an iptables rule to allow incoming connections to your '''SMTP''' server on your '''centos2''' vm.</li>
<li>Once you open the port in the firewall, retry the '''nc''' command. You should get a different error this time (e.g. '''connection refused'''). This time the problem is that your service isn't listening on the outside interface, it's currently configured to listen only on the loopback (lo) interface.</li>
<li>Add the iptables rule to your saved script so that it will be loaded automatically from startup.</li>
</ol>