Environment variables are not yet properly supported for HTML templates.
If you add this to your HTML form:
and you've specified that you want both plain text and HTML, then you'll get the environment variables in the plain text version.
<input type="hidden" name="env_report" value="REMOTE_HOST,REMOTE_ADDR,HTTP_USER_AGENT,AUTH_TYPE,REMOTE_USER" />
If you've specified NoPlain and are only receiving HTML, then the environment variables are appended to the HTML email, but after the </html> tag.
Whether you can see them or not depends on your mail reader. If you look at the email source, then you should see it all there.
Proper support for env. vars. in HTML templates is on our TO-DO list.