[Dovecot] help for static user

[JC]

Hi everybody, 

I have been long (for 2 days) trying, but I really need some help. 
I would like to use virtual static users.

I configured my file as indicated in the documentation and then I
created the following directory, with the needed rights (mail account)
and leave them empty : 
/var/mail/virtual/<mon_domaine>.fr/toto/ 

I am not sure that it is the good method, but I understand it as
follows : dovecot looks up in the directories and takes them as
usernames and domain names. 

When I try to open the imap box from a client (evolution), I get a
"Unknown error - the server closed the connection" message, that doesn't
appear in the server's syslog. 

My dovecont.conf : 
<< 
base_dir = /var/run/dovecot/ 
protocols = pop3s imaps 
imap_listen = *:143 
pop3_listen = * 
ssl_cert_file = /etc/ssl/certs/dovecot.pem 
ssl_key_file = /etc/ssl/private/dovecot.pem 
disable_plaintext_auth = yes 
log_path = /var/log/dovecot.log 
log_timestamp = "%b %d %H:%M:%S " 
login_dir = /var/run/dovecot/login 
login_chroot = yes 
login = imap 
login_executable = /usr/lib/dovecot/imap-login 
login_user = dovecot 
login_process_size = 32 
login_process_per_connection = yes 
login_processes_count = 3 
login_max_processes_count = 128 
login_max_logging_users = 256 
login = pop3 
login_executable = /usr/lib/dovecot/pop3-login 
max_mail_processes = 1024 
verbose_proctitle = yes 
first_valid_uid = 8 
last_valid_uid = 0 
first_valid_gid = 1 
last_valid_gid = 0 
mail_extra_groups = mail 
client_workarounds = outlook-idle outlook-pop3-no-nuls 
mailbox_check_interval = 0 
mailbox_idle_check_interval = 30 
mail_full_filesystem_access = no 
mail_max_flag_length = 50 
mail_save_crlf = no 
mail_read_mmaped = no 
maildir_stat_dirs = no 
maildir_copy_with_hardlinks = no 
maildir_check_content_changes = no 
mbox_lock_timeout = 300 
mbox_dotlock_change_timeout = 30 
umask = 0077 
imap_executable = /usr/lib/dovecot/imap 
imap_process_size = 256 
imap_use_modules = no 
imap_modules = /usr/lib/dovecot/imap 
pop3_executable = /usr/lib/dovecot/pop3 
pop3_process_size = 256 
pop3_use_modules = no 
pop3_modules = /usr/lib/dovecot/pop3 
auth = cram-md5 
auth_mechanisms = cram-md5 
auth_realms = 
auth_userdb = passwd static uid=8 gid=8 home=/var/mail/virtual/%d/%u 
auth_passdb = passwd-file /etc/dovecot/cram-md5.pwd 
auth_user = dovecot 
auth_chroot = 
auth_executable = /usr/lib/dovecot/dovecot-auth 
auth_process_size = 256 
auth_count = 1 
auth_username_chars =
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@ 
>> 

Thank you in advance for any help.