[Dovecot] TROUBLES WITH dovecot configuration

[Alexey S. Kuznetsov]

Hello!
  I'm new in this list and new to dovecot, so I have some troubles with its configuration.
  I have an Linux OS installed and Postfix what supports virtual domains and places mail
  to: /var/spool/mail/vhosts/DOMAIN_NAME/

   I've installed dovecot, configured it to use only pop3 proto. Configuration like this (most important lines from config)
  # cat /usr/local/dovecot/etc/dovecot.conf
  login_user = dovecot
  default_mail_env = mbox:/var/spool/mail/vhosts/%d/%n
  auth = default
  auth_mechanisms = plain
  auth_userdb = passwd-file /usr/local/dovecot/ps/pop.users
  auth_passdb = passwd-file /usr/local/dovecot/ps/pop.users
  auth_user = root

  cat /usr/local/dovecot/ps/pop.users
  testemail at mydomain.org:1a1dc91c907325c69271ddf0c944bc72[34]:1000:7266::/var/spool/mail/vhosts/mydomain.org/:::

  My system uid is 508, when I set it in pop.users file it works nice: accepts password,
  lists mail, everything.
  But when I want to create uniq. id for my domain:
  
  useradd -d /dev/null -s /bin/date -u 1000 mydomainorg
  
  telnet localhost 110
  Trying 127.0.0.1...
  Connected to localhost.localdomain.
  Escape character is '^]'.
  +OK dovecot ready.
  user testemail at mydomain.org
  +OK
  pass pass
  +OK Logged in.
  -ERR No INBOX for user.
  Connection closed by foreign host.

And in logs:

# cat /var/log/dovecot.log
Jan 28 22:11:02 Error:
mkdir_parents(/var/spool/mail/vhosts/mydomain.org//mail/.imap/INBOX)
failed: Permission denied
pop3(testemail at mydomain.org): Jan 28 22:11:02 Error: Couldn't
open INBOX: Internal error occured. Refer to server log for more
information. [2005-01-28 22:11:02]

If I set uid 508 everything will be cool!
I don't understand why it works like this?
I logged in to my account and via sudo su - I became root user.
Root has uid 0, and why it works with uid 508 I can't even imagine :(

Please help me with this problem.
Thanx!

-- 
Sincerely,
Alexey S. Kuznetsov
AK2351-RIPE