title: Changing Port Number for OpenSMTPD
body: <p>I am trying to telnet to my OpenSMTPD 6.0 mail server (Ubuntu 19), but I am consistently getting the error message:</p>
  
  <pre><code>telnet mymachine.xyz.com 25
  telnet: connect to address XX.XX.XX.XX: Connection refused
  </code></pre>
  
  <p>I went through other tutorials and few of them said that it may be because my ISP would be blocking port 25. Now, I think I should now change the port number of OpenSMTPD to a new port number so that I can do a telnet. I have already allowed the port number through the firewall.</p>