title: Search gmail api by custom header
body: <p>I am trying to search gmail api with custom header (this case it is named  <em>notification-id</em>), but it does not work. Request I am making:</p>
  
  <pre><code>GET https://www.googleapis.com/gmail/v1/users/tme/messages?includeSpamTrash=true&amp;q=notification-id%3A560d01cef318893c3c000016
  </code></pre>
  
  <p>I tried the same query using default header (<em>rfc822msgid</em>) from google mail api and it works with this request:
  <code>GET https://www.googleapis.com/gmail/v1/users/me/messages?includeSpamTrash=true&amp;q=rfc822msgid%3A560d01d068c_6690c6f31857290%40ip-172-31-12-127.mail</code></p>
  
  <p>Any ideas why it does not work with custom header?</p>