[Dovecot] Couldn't drop privileges

[CM Reddy]

Hi All,
I have configured the dovecot from sources based on the instructions in the
following link.
http://wiki2.dovecot.org/CompilingSource

Tried to test the installation:
1. Started dovecot successfully.
2. Failed to Login command with an error.

-Lenovo-G500s:~$ telnet localhost 143
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE
AUTH=PLAIN] Hi Dovecot ready.
a login armor5 abc123
* BYE Internal error occurred. Refer to server log for more information.
Connection closed by foreign host.

Configuration is:
------------------------
 Lenovo-G500s:~$ doveconf  -n
# 2.2.10: /usr/local/etc/dovecot/dovecot.conf
# OS: Linux 3.8.0-29-generic x86_64 Ubuntu 12.04.3 LTS
auth_debug = yes
auth_verbose = yes
base_dir = /var/run/dovecot/
disable_plaintext_auth = no
login_greeting = Hi Dovecot ready.
mail_location = mbox:~/mail:INBOX=/var/mail/%u
mail_privileged_group = mail
namespace inbox {
  inbox = yes
  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 = scheme=CRYPT username_format=%u /etc/dovecot/users
  driver = passwd-file
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
userdb {
  args = username_format=%u /etc/dovecot/users
  driver = passwd-file
}


Log information:
----------------------
Jan 13 16:42:34 cmreddy-Lenovo-G500s dovecot: auth: Debug: auth client
connected (pid=5166)
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug: client in:
AUTH#0111#011PLAIN#011service=imap#011secured#011session=+CqxJ9jvkgB/AAAB#011lip=127.0.0.1#011rip=127.0.0.1#011lport=143#011rport=33682#011resp=<hidden>
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug:
passwd-file(armor5,127.0.0.1,<+CqxJ9jvkgB/AAAB>): lookup: user=armor5
file=/etc/dovecot/users
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug: client passdb
out: OK#0111#011user=armor5
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug: master in:
REQUEST#0111108344833#0115166#0111#011d026da1fc2ca16d0208eec7bc369ac2d#011session_pid=5169#011request_auth_token
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug:
passwd-file(armor5,127.0.0.1,<+CqxJ9jvkgB/AAAB>): lookup: user=armor5
file=/etc/dovecot/users
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: auth: Debug: master userdb
out:
USER#0111108344833#011armor5#011uid=1001#011home=/home/armor5#011auth_token=555c47f35a67f94f519da93affe91abef29550fb
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: imap-login: Login:
user=<armor5>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=5169,
secured, session=<+CqxJ9jvkgB/AAAB>
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: imap(armor5): Error: user
armor5: Couldn't drop privileges: User is missing GID (see mail_gid setting)
Jan 13 16:42:44 cmreddy-Lenovo-G500s dovecot: imap(armor5): Error: Internal
error occurred. Refer to server log for more information.

Please help in resolving this issue.
- Thanks
CM Reddy