title: 550 Requested action not taken: mailbox unavailable or not local
body: <p>Have set up a small website for a client however contact form submissions are not getting through to their email address.</p>
  
  <p>The bounce back has this message attached: </p>
  
  <pre><code>550 Requested action not taken: mailbox unavailable or not local
  </code></pre>
  
  <p>It sends without issue to my email address and others but can't get to any on their domain.</p>
  
  <p>Client's IT guy is a bit clueless so I'm unsure how he's configured the mail server?</p>