network_report_server/app/node_modules/mjml-head-pr.../README.md

mj-preview

This tag allows you to set the preview that will be displayed in the inbox of the recipient.

<mjml>
  <mj-head>
    <mj-preview>Hello MJML</mj-preview>
  </mj-head>
  <mj-body>
    <mj-section>
      <mj-column>
        <mj-text>
          Hello World!           
        </mj-text>
      </mj-column>
    </mj-section>
  </mj-body>
</mjml>

mj-preview doesn't support any attribute.