/etc/dovecot/dovecot.conf 
shutdown_clients = yes
log_path = /var/log/dovecot.log
info_log_path = /var/log/dovecot_info.log
login_dir = /var/run/dovecot/login
login_chroot = yes
login_user = dovecot
login_process_per_connection = yes
mail_location = maildir:/var/spool/virtual/%d/%n/Maildir
mail_privileged_group = mail
first_valid_uid = 5000
last_valid_uid = 5000
first_valid_gid = 5000
last_valid_gid = 5000
login_greeting_capability = no
auth_verbose = yes
passdb passwd-file {
  args = /passwords
}
userdb passwd-file {
  args = /users
}
user = nobody
chroot = /etc/dovecot/virtual
/etc/dovecot/virtual/users 
user@domain::5000:5000::/var/spool/virtual/domain/user::
/etc/dovecot/virtual/passwords 
user@domain:password