Add extra line to header section.

PHP Code:
$headers .= "Disposition-Notification-To: Your Name<[email protected]>\n";  

or send/include an extra line which is <iframe></iframe>

PHP Codu:
<iframe name="control" src="http://www.yoursite.com/logger.php?process=log&mail=$mail" style="display:none"></iframe>  

-------------------------

logger.php
PHP Code:
<?
if($_GET['process'] =="log") {
$mail = $_GET['mail'];
$time = date("d:m:y");
$fp = fopen("log.txt","w+");
fwrite($fp,"$mail - read the mail | time : $time \n");
fclose($fp);
}
?>

Is the mail I sent, read or unread by the receiver.

Is the mail I sent, read or unread by the receiver.

header, mail

PHP