[Dovecot] ChgrpNoPerm issue

[Robert JR]

I have dovecot version 2.0.9 

I am confused about this article
http://wiki2.dovecot.org/Errors/ChgrpNoPerm 

my mail_location =
mbox:~/mymail:INBOX=/var/mail/%u 

So my inbox is at var/mail/ and my
imap folder is /home/user/mymail 

The problem is /var/mail (Owner is
useraccount and the group us mail) , and here comes the problem
Dovecot
keeps trying to chown the imap folder inside the homedirectory with
user:mail account and since
And this is the reason of error that appears
in my log file. 

The option mail_access_groups=mail solve the problem..
but I read it is not secure..
With my current configutation, users login
with imap to read mail , can they use
any the mail_access_groups=mail
and read other poeple mail ? does my configutation
is a shard mailbox
and could be unsecure.. 

my main quesion , for my current configuration
, can i use mail_access_groups=mail safely or can
some user use this to
read other people mail ? attached my configuration. 

why didnot have
this issue with uw-imapd? and why dovecot try to chown the .imap 
folder
with the mail group ? 

dovecot -n output is 

# 2.0.9:
/etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-279.2.1.el6.x86_64 x86_64
CentOS release 6.3 (Final) 
disable_plaintext_auth = no
mail_debug =
yes
mail_location = mbox:~/mymail:INBOX=/var/mail/%u
mbox_write_locks =
fcntl
passdb {
 driver = pam
}
ssl_cert =
</etc/pki/dovecot/certs/dovecot.pem
ssl_key =
</etc/pki/dovecot/private/dovecot.pem
userdb {
 driver =
passwd
}
protocol pop3 {
 pop3_uidl_format = %08Xu%08Xv
}
[ 
 Robert