title: mailto link is blocked as insecure content in Chrome Gmail
body: <p>I've got a link in an encrypted HTML email that goes to mailto:blahblah, but it's being blocked in Chrome Gmail.  Anything I can do about this? </p>
  
  <p>Example:</p>
  
  <p>1) I open an <strong>encrypted</strong> HTML email message inside of my <strong>encrypted</strong> GMail web client (<a href="https://gmail.com" rel="noreferrer">https://gmail.com</a> - notice the <strong>s</strong> in https).</p>
  
  <p>2) The email contains a link in the folloiwng format: <code>&lt;a href="mailto:user@example.com"&gt;Email the user.&lt;/a&gt;</code></p>
  
  <p>3) I click on the link, but it is blocked because GMail and/or Chrome is treating the mailto link as insecure content.</p>
  
  <p>4) I add <code>target="_blank"</code> to the aforementioned link and the problem goes away.</p>
  
  <p>The rest of the message displays and functions correctly because, again, both the message <em>and</em> my email client are using encryption.  The only thing that does not work is the mailto link.</p>
  
  <p>Bonus question: how are mailto links classified with regard to protocols such as HTTP and HTTPS?  Links to a W3C document would be helpful.</p>