linux - Dovecot error ChgrpNoPerm

Today I installed Dovecot from source and after configuration and some testing I got error ChgrpNoPerm, which is described here. After reading and misunderstanding I recursively chmod-ed /var/spool/mail/ (mail directory) to 777 and I haven't got any error anymore. Was chmod-ing directory bad solution? Here is my configuration, in case problem is there.

# 2.0.13: /usr/local/etc/dovecot/dovecot.conf
# OS: Linux 2.6.32.25 x86_64 Slackware 13.1.0 simfs
disable_plaintext_auth = no
listen = *
mail_location = mbox:/var/spool/mail:INBOX=/var/spool/mail/%u
passdb {
  driver = shadow
}
protocols = imap pop3
ssl_cert = 
ssl_key = syslog_facility = dovecot
userdb {
  driver = passwd
}