问Cron不发送PHP电子邮件

EN

<?
$dir = './var/session';
$fi = new FilesystemIterator($dir, FilesystemIterator::SKIP_DOTS);
$fileCount = iterator_count($fi);

//    echo 'Directory Count: ';echo $fileCount;

//echo '<br />';



$bytes = 0;
foreach (new DirectoryIterator('./var/session') as $file) {
    if ($file->isFile()) {
        $bytes += $file->getSize();
    }
}

//echo $bytes;
//echo ' Bytes';
//echo '<br />';

 $MBbytes = number_format($bytes / 1048576, 2);
//echo $MBbytes;echo ' MB';



    $from = "mail@example.com";
    $to = "admin@example.com";
    $subject = "Session MB = " .$MBbytes;
    $message = "Session MB = " .$MBbytes."\n Directory Count: " .$fileCount;
    $headers = "From:" . $from;
    mail($to,$subject,$message, $headers,"-fmail@example.com");
//    echo "Email sent";