[Dovecot] antispam - Unable to determine the destination user

[Romanczyk Guillaume]

Hello,
I'm trying to install dovecot antispam plugin and I've some problems 
with dspam user.
When I move a mail out of 'SPAM' folder I have this error in my 
/var/log/messages :

  Oct 28 17:01:41 tony2 imap: antispam: /usr/bin/dspam --source=error 
--class=innocent --signature=47de4679174462472577556 ...
  Oct 28 17:01:41 tony2 dspam[24313]: Unable to determine the 
destination user
  Oct 28 17:01:41 tony2 dspam[24313]: DSPAM agent misconfigured: aborting

I've tried to install it by 'emerging' and compiling from sources but 
with the same result.

plugin .config :

  BACKEND=dspam-exec
  DOVECOT=/usr/include/dovecot
  INSTALLDIR=/usr/lib/dovecot/imap
  USER=vpopmail       
  GROUP=vpopmail
  #(same result with different user/group)
  antispam_dspam_args = --user;$EXT@$USER
  DEBUG=syslog
  DEBUG_VERBOSE=1
  PLUGINNAME=antispam

Mail server configuration :
- NetQmail  (1.05-r8)
- Vpopmail (5.4.16)
- Dovecot     (1.1.4-r1)
- dspam       (3.8.0-r13)
All these packages are emerge without mysql support.

If someone is able to give me some help...

-- 
Guillaume Romanczyk
Itaapy <http://itaapy.com>             Tel +33 (0)1 42 23 67 45
9 rue Darwin, 75018 Paris              Fax +33 (0)1 53 28 27 88