title: Display inline image attachments with wp_mail
body: <p>I have a problem.</p>
  <p>I would like to attach an image to an email and also display it inline, with some other php-generated content. The problem is I don't have the slightest ideea how to use inline a file attachment array used by wp_mail to attach.</p>
  <p>My solution was to encode the images in base64 and put them inline the HTML like this:</p>
  <pre><code>&lt;img alt=&quot;The Alt&quot; src=&quot;data:image/png;base64,*etc*etc*etc&quot; /&gt;
  </code></pre>
  <p>But the problem is that Gmail / Outlook remove the src data from the image. So it lands as</p>
  <pre><code>&lt;img alt=&quot;The Alt&quot; /&gt;
  </code></pre>
  <p>Any clues what to modify (headers to work with base64) or how to use attachment to embed them inline?</p>