title: Sending mail with SMTP to multiple addresses: relaying the message to different servers?
body: <p>I'm sending an email to the following recipients:
  <code>test@example.com</code>, <code>test1@test.com</code>, <code>test2@test.com</code></p>
  
  <p>The message is sent to my local smtp server that has to relay it to <code>@example.com</code> and <code>@test.com</code>.</p>
  
  <p>My question is: how the server should do it ?</p>
  
  <ul>
  <li><p>Leave the message as is and relay it to a more sophisticated smtp server that will do one of the other options</p></li>
  <li><p>Break it into two messages and relay one message to <code>@exampl</code>e and two others to <code>@test.com</code> in one message</p></li>
  <li><p>Break it into three messages and relay once to <code>@example.com</code> and twice to <code>@test.com</code></p></li>
  </ul>
  
  <p>And how the receiving server, for example <code>@example.com</code> know it should not send the <code>@test.com</code> message by himself too? (any mail header?)</p>
  
  <p>What if <code>@example.com</code> and <code>@test.com</code> are served by the same server, will it receive the message more than once?</p>
  
  <p>I'm probably missing something in the SMTP protocol.</p>