[Mimedefang] SA can't find header inserted by MD

[Cahya Wirawan]

Hi,
Actually I want to have SpamAssassin's whitelisting based on envelope sender 
and envelope recipient, and because my sendmail don't write envelope sender
and envelope recipient I inserted 2 headers with mimedefang, I do it in 
filter_sender and filter_recipient:

sub filter_sender {
  my ($sender, $ip, $hostname, $helo) = @_;
  $XEnvelopeFrom = $sender;
  return ('CONTINUE', "ok");
}  
sub filter_recipient {
  my ($recipient, $sender, $ip, $hostname, $first, $helo,
     $rcpt_mailer, $rcpt_host, $rcpt_addr) = @_;
  $XEnvelopeTo = $recipient;
  return ('CONTINUE', "ok");
}

and in filter_end I insert this to variable as X-Envelope-From and 
X-Envelope-To header:

sub filter_end ($) {
  my($entity) = @_;
  ...
  action_add_header("X-Envelope-From","$XEnvelopeFrom");
  action_add_header("X-Envelope-To","$XEnvelopeTo");

  if ($Features{"SpamAssassin"} && !isLocalSender($RelayAddr)) {
  ...
  }
  ...
}

And if I test it I can see that this two new header is correctly
inserted in to email header, but SpamAssassin can't find this 2 new header,
it seems that SA only read the original header, and not any header inserted by
MD, is this normal behaviour or did I do something wrong?

thanks for any help,
Cahya.