I'm trying to make a contact form in HTML page. I've linked it with a .php file and but both on a server but I don't receive any email. Someone can see my mistake?
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Contact form tutorial</title>
</head>
<body>
  <main>
    <p>SEND EMAIL</p>
    <form action="contactform.php" method="post">
      <input type="text" name="name" placeholder="Full name">
      <input type="text" name="mail" placeholder="Your e-mail">
      <input type="text" name="subject" placeholder="subject">
      <textarea name="message" placeholder="Message"></textarea>
      <button type="submit" name="submit">SEND MAIL</button>
    </form>
  </main>
</body>
</html><?php 
if (isset($_POST['submit'])) { 
    $name = $_POST['name']; 
    $subject = $_POST['subject']; 
    $mailFrom = $_POST['mail']; 
    $message = $_POST['message']; 
    $mailTo = "MINE@EMAIL.COM"; 
    $headers = "From: ".$mailFrom; 
    $txt = "You have received an e-mail from ".$name.".\n\n" . $message;
    mail($mailTo, $subject, $txt, $headers); 
    header("Location: index.php?mailsend"); }
 
     
    