Missing html tags in newsletter preview

Hi,

I’ve created several newsletters and the editor works fine. I can see the html code and it is correct. But when I preview them, some html tags are missing.

If I create a newsletter with the next html code:

<h1>This is a title</h1>
<p>This is a paragraph</p>

when I click the preview link, my browser renders the next html code:

<tr>
  <td width="600" style="min-width:600px;" valign="top" align="left">
      This is a title This is a paragraph
  </td>
</tr>

I`ve tried to disable all plugins but it does not work.

Any ideas?

Thanks

https://www.ads-software.com/plugins/wysija-newsletters/