Php mail script not working on my server

Question

<?php  
  //Email information
  $admin_email = "emial id";

  $name = $_REQUEST['name'];

  $email = $_REQUEST['email'];

  $subject = $_REQUEST['subject'];

  $comment = $_REQUEST['message'];

  //send email

  mail($email, "$subject", $comment, "From:" . $admin_email); 
?>

please tell me where is the issues in script