title: Does all SMTP communication happen over 25?
body: <p>Does all SMTP communication send emails between domains on port25? Is all communication unsecured?
  Understand that using like Gmail communication is secured to Gmail server but after it must use unsecured port 25, right?</p>
  
  <p>SMTP can be on any port, but that is not what i am talking about. I am not talking about connecting to Gmail, Yahoo or ISP SMTP server. Those are the SMTP relays and they accept SMTP requests on any port they wish encrypted/unencrypted for their user. </p>
  
  <p>But once SMTP relay server gets request, mail server forwards it to email based on domain name MX record. Does it only use SMTP on port 25? The mail server has only knowledge of domain name and then forwards it. It can not know which port they are listening.</p>
  
  <p>For example, I am hosting an Exchange server 2007 for my domain. I connect to my Exchange server to send mail to xyz@gmail.com. My exchange server must be doing communication over industry standard protocol, right? And that's port 25 (as my Exchange server didn't work without port 25).</p>