<?php
  include ("header.php");
  
  if ($jump == "Verschicken") {     
     $query = mysql_query("SELECT klammid,email,verdienst,username,ausgezahlt,anbieter FROM teilnehmer WHERE ausgezahlt='Ja'") or die (mysql_error());
     
     while ($newsletter = mysql_fetch_assoc($query)) {
        $i++;
        echo "Mail $i ";
        mail("".$newsletter['email']."", "$betreff", "
        $text\n
        ","From: $projekturl<$webmastermail>");
     }
     die();
  }
  
  echo "<form name='FormName' action='newsletter.php' method='post'>
        <table width=\"50\" border=\"0\" cellspacing=\"0\" cellpadding=\"0\">
        <tr>
           <td><font size=\"2\">Betreff:</font></td>
           <td><input type=\"text\" name=\"betreff\"></td>
        </tr>
        <tr>
           <td><font size=\"2\">Text:</font></td>
           <td><textarea rows=\"22\" name=\"text\" cols=\"89\"></textarea>
        </tr>
        <tr>
           <td colspan=\"2\"><input type=\"submit\" name=\"jump\" value=\"Verschicken\"></td>
        </tr>
        </table>
        </form>";
 
  include ("footer.php");
?>

<?php
 ...

$hash = array ();
while ($newsletter = mysql_fetch_assoc($query)) {
    $recipient = strtolower ($newsletter['email']);
    if (!array_key_exists ($recipient, $hash)) {
        $i++;
        echo "Mail $i ";
        mail("".$newsletter['email']."", "$betreff", "
        $text\n
        ","From: $projekturl<$webmastermail>");
        ++$hash[$recipient];
    }
}

...
?>