<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 - it shouldn't.</li><li>Issue an iptables rule to allow incoming connections to '''TCP port 25'''.</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>