I can’t understand why the script works on some hostings, on some it doesn’t. What could be the problem?

Question

PHP

On hosts where this script does not work and changed PHP versions, the mail sending function is enabled, simple letters arrive, but when you add, as I assume, additional headers for sending files, everything stops working. On some hosts the script works

<?php
if (isset ($_POST['contactFF'])) {
  $to = "[email protected]"; // поменять на свой электронный адрес
  $from = $_POST['contactFF'];
  $subject = "Заполнена контактная форма с ".$_SERVER['HTTP_REFERER'];
  $message = "Имя: ".$_POST['nameFF']."\nEmail: ".$from."\nIP: ".$_SERVER['REMOTE_ADDR']."\nСообщение: ".$_POST['messageFF'];
  $boundary = md5(date('r', time()));
  $filesize = '';
  $headers = "MIME-Version: 1.0\r\n";
  $headers .= "From: " . $from . "\r\n";
  $headers .= "Reply-To: " . $from . "\r\n";
  $headers .= "Content-Type: multipart/mixed; boundary=\"$boundary\"\r\n";
  $message="
Content-Type: multipart/mixed; boundary=\"$boundary\"

--$boundary
Content-Type: text/plain; charset=\"utf-8\"
Content-Transfer-Encoding: 7bit

$message";
  for($i=0;$i<count($_FILES['fileFF']['name']);$i++) {
     if(is_uploaded_file($_FILES['fileFF']['tmp_name'][$i])) {
         $attachment = chunk_split(base64_encode(file_get_contents($_FILES['fileFF']['tmp_name'][$i])));
         $filename = $_FILES['fileFF']['name'][$i];
         $filetype = $_FILES['fileFF']['type'][$i];
         $filesize += $_FILES['fileFF']['size'][$i];
         $message.="

--$boundary
Content-Type: \"$filetype\"; name=\"$filename\"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=\"$filename\"

$attachment";
     }
   }
   $message.="
--$boundary--";

  if ($filesize < 10000000) { // проверка на общий размер всех файлов. Многие почтовые сервисы не принимают вложения больше 10 МБ
    mail($to, $subject, $message, $headers);
    echo $_POST['nameFF'].', Ваше сообщение получено, спасибо!';
  } else {
    echo 'Извините, письмо не отправлено. Размер всех файлов превышает 10 МБ.';
  }
}
?>

Answer 1

compare phpinfo to hosting where it works and doesn't work