It would be hard to give exact line numbers for where the edits should be, as I have some other modifications in place as well. But this should be enough info to figure it out:
- In 'include/class.ticket.php' look for this line:
$email->send($ticket->getEmail(),$subj,$body);
Put this code on a new line right after the code above:
$ticket->postNote('Auto-Response: '.$subj,$body,false, "System");