Sorry about that, it is just like the error says, there is an extra ) at the end of the function call. You should update this line of code to be like this instead:
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader, "-f" . "".((isset($_POST["Email_address"]))?$_POST["Email_address"]:"") ."");
That is what I get for cutting and pasting, I'll be paying more attention next time.