mj-wrapper-full-width-section-background.mjml

<mjml>
  <mj-body>
    <mj-wrapper>
      <mj-section full-width="full-width" background-url="https://example.com/image.jpg" background-size="cover" background-repeat="no-repeat">
        <mj-column>
          <mj-text>Hero section</mj-text>
        </mj-column>
      </mj-section>
      <mj-section background-color="#ffffff">
        <mj-column>
          <mj-text>Regular section</mj-text>
        </mj-column>
      </mj-section>
    </mj-wrapper>
  </mj-body>
</mjml>