[Yellow Slider]

Well, you're gonna have to create a plugin such as this:
Hook Location: mail_start
PHP Code:

PHP Code:

if ($vbulletin->session->vars['notificationemail'])
{
    $headers .= 'Content-Type: text/html' . iif($encoding, "; charset=\"$encoding\"") . $delimiter;
} 


Then you'd have to put the following line of code everywhere notifications are sent:

PHP Code:

$vbulletin->session->vars['notificationemail'] = true; 


For example, in the hook location newpost_notification_start.