[Exim] saving spam

Lo all,

I'm trying to store each individual user's spam into a separate mailbox that
only that have access to. Using spamassissin, I've setup a basic filter to
catch the messages using the subject prefix...

system.filter:
# Mail flagged as spam by spam assasin.
if first_delivery and
   $h_X-Spam-Flag: contains "YES"
then
   logfile /var/log/exim/spam.log
   logwrite "$tod_log From: $h_From: Subject: $h_Subject: \n \t
X-Spam-Status: $h_X-Spam-Status: Sender: $sender_address"
   save /var/spool/mail/$domain/$local_part-spam/
#   if $h_From: is not ""
#   then
#      mail to $h_From: subject "Re: Your last message to me"
#           expand file /usr/local/etc/exim/spamreply.txt
#           once /var/log/exim/spamcount
#           once_repeat 5d
#   endif
   seen finish
endif

This, does not work :-(

I've also tried in exim.conf:
message_filter_directory_transport = spam_delivery

And the transport:
spam_delivery:
driver = appendfile
no_from_hack
prefix = ""
suffix = ""
maildir_format
create_directory
directory = "/var/spool/mail/${lc:$domain}/${lc:$local_part}-spam/"
user = exim
group = exim
mode = 0660


But that too, doesn't work...

Does anyone have some ideas for me how to get this working?