将密件抄送添加到现有的PHP表单

Question

我有发送电子邮件的现有php表单。我现在想在发送的电子邮件中添加密件抄送，是否有一种方法可以修改代码以便发送密件抄送？

            # email headers.
        $headers = "From: $name <$email>";

        # Send the email.
        $success = mail($mail_to, $subject, $content, $headers);
        header('Location: thank-you');
        if ($success) {