title: Status 503: is "Retry-After" necessary?
body: <p>I'm adding to my php script a 503 header statement. In all examples I've seen, this is followed by some variation of:</p>
  
  <pre><code>header('Retry-After: 300');
  </code></pre>
  
  <p>Is it necessary to include the "Retry-After" statement? I'd prefer not to.</p>