function check_data() {
  var fehlertxt="";
  var checked=true;
  
  var re_email=/^([a-zA-Z0-9\.\_\-]+)@([a-zA-Z0-9\.\-]+\.[A-Za-z][A-Za-z]+)$/;
  
  var f_name = document.contact_form.c_name.value;
  var f_tel = document.contact_form.c_tel.value;

  var f_email = document.contact_form.c_email.value;
  var f_msg = document.contact_form.c_msg.value;
  
  
  
  if(f_name.length<4) { fehlertxt +="Name kontrollieren! \n"; checked=false; }
  if(f_tel.length<8) { fehlertxt +="Telefon kontrollieren! \n"; checked=false; }
  if(f_msg.length<8) { fehlertxt +="Bitte eine Nacricht eingeben! \n"; checked=false; }



  
  
  if((re_email.test(f_email))==false || f_email.length==0) {
   fehlertxt +="Emailadresse kontrollieren!\n";
   checked=false;
  }
  
  if(checked==false) {
   alert(fehlertxt);
  }
   else {
    document.contact_form.method="POST";
    document.contact_form.action="<?=$_SERVER['PHP_SERVER']?>";
    document.contact_form.submit();
   }
    return checked;
 }