Mail system php

PHP kode 

 if($_POST['submit']) {
     $to = $_POST['to'];
     $to_name = $_POST['to_name'];
     $message = htmlspecialchars($_POST['message']);
     /* TID */
     $time = time();
     $tid = date("H:i");
     $dag = date("d", $time); 
     $number = date("n", $time); 
     $maaned = array(1=>"Januar", "Februar", "Marts", "April", "Maj", "Juni", "Juli", "August", "September", "Oktober", "November", "December");
 
     $date = $dag.". ".$maaned[$number]." - ".$tid;
     /* TID */
     $from_name = $_SESSION['fullname'];
     $session_id = $_SESSION['id'];
     mysql_query("INSERT INTO mail (to, to_name, from, from_name, message, date) VALUES ('$to', '$to_name', '$session_id', '$from_name', '$message', '$date')");
     echo "Din besked er nu sendt :)";
 }
 ?>
 <form action='' method='POST'>
     <table width='100%'>
         <tr>
             <td colspan='2'>
                 <h2>Send en besked</h2><hr><br>
             </td>
         </tr>
         <tr>
             <td width='15%'>
                 Til:
             </td>
             <td width='85%'>
                 <select name='to'>
                     <?php
                     $query = mysql_query("SELECT id, fullname FROM user ORDER BY fullname");
                     if(mysql_num_rows($query)) {
                         while ($row = mysql_fetch_assoc($query)) {
                             echo "<option value='". $row['id'] ."'>". $row['fullname'] ."</option>";
                         }
                     }
                     ?>
                 </select>
             </td>
         </tr>
         <tr>
             <td>
                 &nbsp;
             </td>
         </tr>
         <tr>
             <td width='15%'>
                 Besked:
             </td>
             <td width='85%'>
                 <textarea name='message' cols='59' rows='12'></textarea>
             </td>
         </tr>
         <tr>
             <td>
                 &nbsp;
             </td>
         </tr>
         <tr>
             <td width='10%'>
                 <input type='submit' name='submit' value='Tilføj'><br><br><br><br><br><br>
             </td>
         </tr>
     </table>
 </form>