'''Perform the following steps:'''

Connect from your server We will be demonstrating the use of the telnet application to your server using telnet:test that the postfix service is running.

# Connect from your server to your server using telnet by issuing the following command:<br><source lang="bash">telnet localhost 25</source># Note that it will tell should indicated that you once your connect that are connected by displaying the the text:'''Escape character is '^]''', which means your indicates that in order to end the telnet session, you can hold control and press the square bracket key . Perform that key-combination to end the telnet session (and then .#Enter the command '''exit ''' to close the telnet app)application.

If it worked, this worked - indicates that means the postfix service is running and listening and responding to connections. 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, you'll need to allow incomming connections to TCP port 25.

<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 - try , 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>