<tr>
  <td class="spacer" height="40" style="font-size: 40px; line-height: 40px; margin: 0; padding: 0;">&nbsp;</td>
</tr>

<tr>
  <td class="spacer" height="40" style="font-size: 40px; line-height: 40px; mso-line-height-rule: exactly; padding: 0;">&nbsp;</td>
</tr>

Fix Outlook line-height for inner row spacer.
Fix Outlook line-height for inner row spacer.
