title: How to send email with Phpmailer with DKIM signature?
body: <p>I`m using PHPmailer to sent email.</p>
  
  <p>I installed postfix service and DKIM-Milter to generate the key.</p>
  
  <p>It works fine if i use command line to sent mail, and the mail is with DKIM signature displaying "signed-by:mydomain.com"</p>
  
  <pre><code>Authentication-Results: mx.google.com; spf=pass (google.com: domain of root@mydomain.com designates 182.50.xxx.xxx as permitted sender) smtp.mail=root@mydomain.com; dkim=pass header.i=@mydomain.com
  
  DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mydomain.com; s=default;
      t=1325531456; bh=+gZFhu4Id2AXb8UVbFLzDVVlChWGhvxvJUIdjdMLQsk=;
      h=To:Subject:Message-Id:Date:From;
      b=mH4GV8ayicc6UMn1uopCc9VJb5v2MiOKQpEtwJjckzoJ8ePhRKQIZI5KnzSdSoSP3
       BtmehOQhMn9kIR/TlL2dlSog2EkRNeAaWcmO1K3khtCZ7rkXHGJsDn9C6l49K0tJa2
       rplPOSI7wS8+3NCEiuc5sjZimPo4v9WuTECVqxkg=
  </code></pre>
  
  <p>But i want to use PHPmailer (5.1) to sent mail with DKIM signature supported, but returns this:</p>
  
  <pre><code>Authentication-Results: mx.google.com; spf=pass (google.com: domain of info@mydomain.com designates 182.50.xxx.xxx as permitted sender) smtp.mail=info@mydomain.com; dkim=neutral (bad format) header.i=info@mydomain.com
  
  DKIM-Signature: v=1; a=rsa-sha1; q=dns/txt; l=70; s=default;
      t=1325533594; c=relaxed/simple;
      h=From:To:Subject;
      d=mydomain.com; i=@mydomain.com;
      z=
      |
      |Subject:=20Testing=20email=20from=20phpmailer;
      bh=lC+16EvauA2HuJG03ArE6CtgLuY=;
      b=
  </code></pre>
  
  <p>I checked the class.phpmailer.php file, and it has some DKIM options:</p>
  
  <pre><code>  public $DKIM_selector   = 'default';
  
    /**
     * Used with DKIM DNS Resource Record
     * optional, in format of email address 'you@yourdomain.com'
     * @var string
     */
    public $DKIM_identity   = '';
  
    /**
     * Used with DKIM DNS Resource Record
     * optional, in format of email address 'you@yourdomain.com'
     * @var string
     */
    public $DKIM_domain     = '';
  
    /**
     * Used with DKIM DNS Resource Record
     * optional, in format of email address 'you@yourdomain.com'
     * @var string
     */
    public $DKIM_private    = '';
  </code></pre>
  
  <p>How to configure this option? I know the public key and private key, but what`s is $DKIM_private and $DKIM_identity?</p>