title: PHPMailer : how to set Content-Type to multipart/alternative
body: <p>I'm sending e-mails with phpmailer but the messages comes with Content-Type: text/html in the header.  how can I change it to multipart/alternative?</p>
  
  <p>it should be something like  $mail-></p>
  
  <p>my config is:</p>
  
  <pre><code>$mail = new PHPMailer();
  
  $mail-&gt;setFrom('mail@mail.com', 'name');
  $mail-&gt;isHTML(true);                                
  $mail-&gt;CharSet = "ISO-8859-1";
  $mail-&gt;XMailer = ' ';
  </code></pre>