Pin Code Confirmation Email: Add Domain

[porter]

Is there anyway that we can add the domain name into the confirmation e-mail that the pin is sent in? If so, what would the code be?

$subject = "Your PIN order";
$message = "Hello {$order['name']},\n\nYour PIN: $pin\n\nOnce again, thank you for your purchase.\n\n";
xtmail($order['email'], $subject, $message);