magic "Confirm Subscription" link in Google Inbox for Mailchimp subscription confirmation email

email.html

<!-- Google Inbox displayed a "Confirm Subscription" link button immediately below the subject line, both when the 
    email was opened and when it was closed. Clicking the button would confirm the subscription without the browser
    visibly opening the confirmation link. -->

<span itemscope itemtype="http://schema.org/EmailMessage">
  <span itemprop="description" content="We need to confirm your email address."></span>
  <span itemprop="action" itemscope itemtype="http://schema.org/ConfirmAction">
    <meta itemprop="name" content="Confirm Subscription">
    <span itemprop="handler" itemscope itemtype="http://schema.org/HttpActionHandler">
      <meta itemprop="url" content="https://carloop.us6.list-manage.com/subscribe/smartmail-confirm?u=...&id=...&e=...&inline=true">
      <link itemprop="method" href="http://schema.org/HttpRequestMethod/POST">
    </span>
  </span>
</span>