title: DKIM signing emails using Postfix with removed headers
body: <p>I have a problem getting OpenDKIM working with Postfix. Due to security reasons we remove certain headers from our emails:</p>
  
  <p>From main.cf:</p>
  
  <pre><code>mime_header_checks = regexp:/etc/postfix/header_checks
  header_checks = regexp:/etc/postfix/header_checks
  </code></pre>
  
  <p>The headers removed are as follows:</p>
  
  <pre><code>/^Received:.*with ESMTPSA/              IGNORE
  /^X-Originating-IP:/     IGNORE
  /^X-Mailer:/             IGNORE
  /^Mime-Version:/         IGNORE
  </code></pre>
  
  <p>However this makes the opendkim fail:</p>
  
  <pre><code>Nov 22 19:26:15 localhost opendkim[5104]: BC4F5406A9: can't determine message sender; accepting
  </code></pre>
  
  <p>Is there any way to have the headers removed <em>and</em> getting opendkim work?</p>