如何用php查看郵件是否已被閱讀？

       當你在發送郵件時，你或許很想知道該郵件是否被對方已閱讀，下面有段不錯的代碼可以實現此需求，喜歡的朋友可以參考下 

代碼如下: <?  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);    ?>