Additional custom email send on submit

I need to email a set of custom form fields (formatted in a specific way) to a separate email address on submit.

For testing purposes I just want to use mail($To, $Subject, $Message, $Headers);

Can anyone confirm the file and line (or roughly where in the file) I need to insert the PHP so it will work.

I have tried the line before

$PPTPayment->InsertOrder(“”,$_POST[‘orderid’],0); (in tpl-add.php)

But this does not work. The mail function is working on my server as I have tried it outside directorypress without issues.