function sendmail(){
  var recipient=prompt("Bitte geben Sie die E-Mailadresse des Empfängers ein:","");
  if(recipient&&recipient!=""&&recipient!="undefined"&&recipient!="null"){
    document.sendmail.loc.value=document.location.href;
    document.sendmail.recipient.value=recipient;
    document.sendmail.submit();
  }
}