Body

A table with the class .body automatically wraps the email content and applies styles to give more consistent layout to the page. You can put classes on the <body> that will be moved onto the body table.

For example this:

...
<body class="bg-light">
  ...
</body>

Becomes this:

...
<body>
  <table class="body bg-light">
    ...
  </table>
</body>