dovecot - Jul 2011 - want only usder in userfile/passfile and use to login user@domain

After adding:

auth_username_format=%Lu

the %d domain is unfolleded correctly. (and not empty anymore)
Maybe a good idee to make a remark in the text Virtual Users about that.

I use:
passdb:
    driver: passwd-file
    args: /etc/dovecot/vhosts/%d/etc/shadow
  userdb:
    driver: static
    args: uid=virtual gid=virtual home=/var/mail/vhosts/%d/%u

In the password-file (shadow) i have to add users in the form
user at domain.
I want to add users in the form user

I have also tryed not a static userdb but a real one; see example 
Dynamic-passwd locations.
To get this working i had to add mail-uid and mail-gid.
But still it has the same form
user at domain and not user

Can anybody tell my how to get ride of the domain part in the passwd en 
userfile. I still want the user to login with user at domain

Thanks.

Erik


Mijn config:
# 1.2.15: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-5-686 i686 Debian 6.0.2 ext4
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imap imaps pop3 pop3s
ssl_cert_file: /etc/ssl/certs/server.crt
ssl_key_file: /etc/ssl/private/server.key
login_dir: /var/run/dovecot/login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
mail_privileged_group: mail
mail_location: maildir:/var/mail/vhosts/%d/%n/Maildir
mail_debug: yes
mbox_write_locks: fcntl dotlock
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
auth default:
  mechanisms: plain login
  username_format: %Lu
  debug: yes
  debug_passwords: yes
  passdb:
    driver: passwd-file
    args: /etc/dovecot/vhosts/%d/etc/shadow
  userdb:
    driver: static
    args: uid=virtual gid=virtual home=/var/mail/vhosts/%d/%u
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth-client
      mode: 432
      user: postfix
      group: postfix