如何用php查看邮件是否已被阅读？

       当你在发送邮件时，你或许很想知道该邮件是否被对方已阅读，下面有段不错的代码可以实现此需求，喜欢的朋友可以参考下 

代码如下:
<? 
error_reporting(0); 
Header("Content-Type: image/jpeg"); 
 
//Get IP 
if (!empty($_SERVER['HTTP_CLIENT_IP'])) 
{ 
$ip=$_SERVER['HTTP_CLIENT_IP']; 
} 
elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) 
{ 
$ip=$_SERVER['HTTP_X_FORWARDED_FOR']; 
} 
else 
{ 
$ip=$_SERVER['REMOTE_ADDR']; 
} 
 
//Time 
$actual_time = time(); 
$actual_day = date('Y.m.d', $actual_time); 
$actual_day_chart = date('d/m/y', $actual_time); 
$actual_hour = date('H:i:s', $actual_time); 
 
//GET Browser 
$browser = $_SERVER['HTTP_USER_AGENT']; 
 
//LOG 
$myFile = "log.txt"; 
$fh = fopen($myFile, 'a+'); 
$stringData = $actual_day . ' ' . $actual_hour . ' ' . $ip . ' ' . $browser . ' ' . "rn"; 
fwrite($fh, $stringData); 
fclose($fh); 
 
//Generate Image (Es. dimesion is 1x1) 
$newimage = ImageCreate(1,1); 
$grigio = ImageColorAllocate($newimage,255,255,255); 
ImageJPEG($newimage); 
ImageDestroy($newimage); 
 
?>