title: What is the effect of a Precendence: bulk header on e-mail messages
body: <p>According to <a href="https://mail.google.com/support/bin/answer.py?answer=81126#format" rel="noreferrer">Google Mail guidelines</a>, bulk mail must contain the header </p>
  
  <pre><code>Precedence: bulk
  </code></pre>
  
  <p>What does it do? I could not find a RFC describing the effect on mail delivery. </p>
  
  <p>Some background: I'm working on scripts that will send 500k+ mails daily. They are different kind of messages: account related mail (delivery critical), but also notifications of new content (delivery not critical).</p>