title: SMTP: inter-server communication
body: <p>As I know the email message sending process looks like this:</p>
  
  <ol>
  <li>The message is sent from sender's client to his server (say <strong>mail.com</strong>).</li>
  <li>The <strong>mail.com</strong> server redirects the message to recipients server (say <strong>gmail.com</strong>).</li>
  <li>Recipient's client connects to <strong>gmail.com</strong> and recieves new messages.</li>
  </ol>
  
  <p>I'm interested in <strong>stage 2</strong>.
  I thought that the servers use SMTP protocol to make this negotiation. And <strong>gmail.com</strong> server should listen to 25 port to recieve a connection from <strong>mail.com</strong> and other servers.</p>
  
  <p>But then I try to connect <strong>gmail.com</strong> (exactly, Google service) on port 25, the server is not responding...</p>
  
  <p>Why? What's wrong?</p>