title: phpmailer don't put in header DKIM informations
body: <p>I'm working to put DKIM signature in the emails sent with a small crm I've created.
  I've insert the public key in the text record of my domain and now I'm working to put private key in phpmailer when I'm sending a email.
  I used the example inside the class:</p>
  
  <pre><code>$mail-&gt;DKIM_domain = 'example.com';
  $mail-&gt;DKIM_private = 'path/to/private.key';
  $mail-&gt;DKIM_selector = 'phpmailer';
  $mail-&gt;DKIM_passphrase = '';
  $mail-&gt;DKIM_identity = $mail-&gt;From;
  </code></pre>
  
  <p>when I send the mail gmail says my dkim signature is PASS. If i test the mail sending it at check-auth@verifier.port25.com I recieve:</p>
  
  <blockquote>
    <p>---------------------------------------------------------- DKIM check details:
    ---------------------------------------------------------- Result:         permerror (hash algorithm used in signature (sha256) ID(s) verified:
    not</p>
  </blockquote>