Hi,
You need to get the parameters for post params before you can use them in your email template.
Suppose that you have {name, email, order, subtotal, promo, tax, shipping, total} fields in your form, you need to write code like below before making MAIL call :
my $query = new CGI;
my $name = $query->param('name');
my $email = $query->param('email');
my $order = $query->param('order');
my $subtotal = $query->param('subtotal');
my $promo = $query->param('promo');
my $tax = $query->param('tax');
my $shipping = $query->param('shipping');
my $total = $query->param('total');