验证域名发送电子邮件

Question

如何向客户发送电子邮件证明发送的电子邮件是从发送电子邮件的域发送的？我已经包含了用于发送电子邮件的代码。

$headers = "From: noreply@mydomain.com\r\n";
$headers .= "Reply-To: noreply@mydomain.com\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";  
$to = $_GET['to'];
$subject = $_GET['subject'];
$message = $_GET['message'];
$headers = "From:" . $from;
mail($to,$subject,$message,$headers);