<ol><li value="4">Let's see if it works from other machines. Telnet to vm2 from the host (connect to the SMTP port) and see if it works. If your firewall is set up properly, the telnet command should not permit a connection.</li><li>Issue Create an iptables rule to allow incoming connections to '''TCP port 25'''your SMTP server.</li><li>Once you open the port in the firewall, retry the '''telnet''' command. You should get a different error this time. 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></ol>