Hi @ghmccord,
I've asked the add-on developers this question The inline style will not work in this case. You should use the wpforo_kses_allowed_html_email hook for this purpose.
Below is an example code, you should add it in your active theme's functions.php file.
add_filter('wpforo_kses_allowed_html_email', 'custom_wpforo_kses_allowed_html_email');
function custom_wpforo_kses_allowed_html_email($allowed_html){
if( !wpfkey($allowed_html, 'h1') ) $allowed_html['h1'] = array();
if( !wpfkey($allowed_html['h1'], 'style') ) $allowed_html['h1']['style'] = array();
if( !wpfkey($allowed_html, 'span') ) $allowed_html['span'] = array();
if( !wpfkey($allowed_html['span'], 'style') ) $allowed_html['span']['style'] = array();
return $allowed_html;
}