These hooks allow the entire content of the email to be filter and amended immediately prior to sending. An example use for the ‘s2_html_email’ hook to add a stylesheet is below.
function my_s2html_filter($message) { if ( empty($message) ) { return; } list($first, $second) = explode('', $message, 2); $message = $first . '' . $second; return $message;}add_filter('s2_html_email', 'my_s2html_filter');