title: ActionMailer email images broken in some clients
body: <p>I'm using ActionMailer to send emails, and these emails include images. To include the images I'm using <code>&lt;%= image_tag('email-logo.png') %&gt;</code> and <code>config.action_controller.asset_host</code> in staging/production is set correctly. </p>
  
  <p>These images appear fine in Outlook (I also tried it in a few temp email services, and they work there as well), but appear broken in Gmail, Apple Mail (desktop + iOS), and Mailbox app.</p>
  
  <p>The encoding for the HTML version of the email is <code>quoted-printable</code>, is that correct?</p>
  
  <p>When I inspect the raw email in Gmail, the markup for the image appears like:</p>
  
  <pre><code>  &lt;img alt=3D"Site Logo" class=3D"logo" src=3D"//staging.mysite.come/ass=
  ets/email-logo-98e7cf6a48a4f2186ab9de2dcdfaa4bf0.png" style=3D"width: 30=
  px; display: inline; vertical-align: middle;" /&gt;
  </code></pre>
  
  <p>When I remove the <code>=</code> and load the URL in my browser it appears fine. Could the <code>=</code> be breaking it? Could it be the lack of protocol in the image URL?</p>
  
  <p>Thanks for any help in advance!</p>