dovecot - May 2012 - Public maiboxes

hello

I'm trying to setup a server with public mailboxes only
but I cannot succeed.

Anyone could help me a bit ? thank you

here is the doveconf -n output

# 2.1.6: /usr/local/etc/dovecot/dovecot.conf
# OS: FreeBSD 7.4-RELEASE-p3 amd64
auth_debug = yes
debug_log_path = /var/log/dovecot/debug.log
disable_plaintext_auth = no
info_log_path = /var/log/dovecot/info.log
log_path = /var/log/dovecot/dovecot.log
mail_debug = yes
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex imap4flags copy include variables body enotify 
environment mailbox date ihave
namespace {
   list = children
   location = maildir:/var/mail/public
   prefix = public.
   separator = /
   subscriptions = no
   type = public
}
namespace inbox {
   location    mailbox Drafts {
     special_use = \Drafts
   }
   mailbox Junk {
     special_use = \Junk
   }
   mailbox Sent {
     special_use = \Sent
   }
   mailbox "Sent Messages" {
     special_use = \Sent
   }
   mailbox Trash {
     special_use = \Trash
   }
   prefix }
passdb {
   args = /usr/local/etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
plugin {
   acl = vfile
   sieve = ~/.dovecot.sieve
   sieve_dir = ~/sieve
}
ssl_cert = </etc/ssl/RENATER/cert-2209-webmail.esiee.fr.pem
ssl_key = </etc/ssl/RENATER/webmail.esiee.fr.key
userdb {
   args = /usr/local/etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
protocol imap {
   mail_plugins = " imap_acl"
}