[Dovecot] Dovecot setuid, setgid, permission denied Problem!

["Яцко Эллад Геннадьевич]

Hello! Please, help!
I have trouble with Dovecot's Deliver utility. I don't know how to avoid 
errors. Let me know what additional related information do you need?

1) Its call in Exim's configure:
==========================================
local_delivery_spam_transport:
  driver               = pipe
  command              = /usr/local/libexec/dovecot/deliver -c 
/usr/local/etc/dovecot/dovecot.conf -d $local_part@$domain -m Junk
  message_prefix       =
  message_suffix       =
  log_output           = true
  delivery_date_add
  envelope_to_add
  return_path_add
  user                 = mailnull
  group                = mail
==========================================

2) maillog output:
==========================================
Nov 13 11:16:50 srvgate-msk exim[47586]: 1N8rKs-000CNW-Qu <= 
eyatsko at runoguy.ru H=main.domain.runoguy.ru [172.16.77.11] P=esmtpa 
A=auth_plain:eyatsko at runoguy.ru S=42548 from <eyatsko at runoguy.ru> for 
eyatsko at runoguy.ru
Nov 13 11:16:51 srvgate-msk exim[47593]: 1N8rKt-000CNd-D2 <= 
eyatsko at runoguy.ru U=mailnull P=spam-scanned S=43507 
id=E1N8rKs-000CNW-Qu at srvgate-msk.runoguy.ru from <mailnull at runoguy.ru> 
for eyatsko at runoguy.ru
Nov 13 11:16:51 srvgate-msk exim[47587]: 1N8rKs-000CNW-Qu => eyatsko 
<eyatsko at runoguy.ru> R=dspam_spamscan_router T=dspam_spamscan_transport
Nov 13 11:16:51 srvgate-msk exim[47587]: 1N8rKs-000CNW-Qu Completed
Nov 13 11:16:51 srvgate-msk deliver(eyatsko at runoguy.ru): auth input: 
home=/var/mail/exim
Nov 13 11:16:51 srvgate-msk deliver(eyatsko at runoguy.ru): auth input: uid=26
Nov 13 11:16:51 srvgate-msk deliver(eyatsko at runoguy.ru): auth input: gid=26
Nov 13 11:16:51 srvgate-msk deliver(eyatsko at runoguy.ru): Fatal: 
setgid(26(mailnull)) failed with euid=26(mailnull), gid=6(mail), 
egid=6(mail): Operation not permitted
Nov 13 11:16:51 srvgate-msk exim[47594]: 1N8rKt-000CNd-D2 == 
eyatsko at runoguy.ru R=local_delivery_spam_router 
T=local_delivery_spam_transport defer (0): Child process of 
local_delivery_spam_transport transport returned 75 (could mean 
temporary error) from command: /usr/local/libexec/dovecot/deliver
==========================================

3) dovecot-mysql.conf
==========================================
driver = mysql
connect = host=localhost dbname=exim user=exim password=*****
default_pass_scheme = PLAIN
password_query = SELECT `username` as `user`, `password` FROM `users` 
WHERE `username` = '%n@%d' AND `active`='Y'
user_query = SELECT `home`, 26 AS `uid`, 26 AS `gid` FROM `users` WHERE 
`username` = '%n@%d' AND `active`='Y'
==========================================

4) Owner and permissions on mailbox-directory:
==========================================
/usr/local/etc/exim> ll /var/mail/exim/runoguy.ru/
total 6
drwxrwx---  10 mailnull  mail  512 Nov 13 10:40 eyatsko
drwxrwx---   5 mailnull  mail  512 Nov 12 22:17 nkolobovnikova
drwxrwx---   5 mailnull  mail  512 Nov 12 22:30 oyatsko
/usr/local/etc/exim>
==========================================

5) Junk folder:
==========================================
/usr/local/etc/exim> ll /var/mail/exim/runoguy.ru/eyatsko/
total 46
drwxrwx---  5 mailnull  mail    512 Nov 10 21:29 .Drafts
drwxrwx---  5 mailnull  mail    512 Nov 10 21:34 .Junk
drwxrwx---  5 mailnull  mail    512 Nov 12 17:24 .Outgoing
drwxrwx---  5 mailnull  mail    512 Nov 12 14:01 .Sent
drwxrwx---  5 mailnull  mail    512 Nov 12 17:24 .Trash
drwxrwx---  2 mailnull  mail   1024 Nov 13 10:40 cur
-rwxrwx---  1 mailnull  mail     17 Nov 10 18:47 dovecot-keywords
-rw-------  1 mailnull  mail     19 Nov 13 10:40 dovecot-uidlist
-rwxrwx---  1 mailnull  mail      8 Nov 10 21:24 dovecot-uidvalidity
-rwxrwx---  1 mailnull  mail      0 Nov 10 17:17 
dovecot-uidvalidity.4af975ff
-rw-------  1 mailnull  mail    384 Nov 13 10:40 dovecot.index
-rwxrwx---  1 mailnull  mail  16916 Nov 13 10:40 dovecot.index.cache
-rw-------  1 mailnull  mail    116 Nov 13 10:40 dovecot.index.log
drwxrwx---  2 mailnull  mail    512 Nov 13 10:33 new
-rwxrwx---  1 mailnull  mail     38 Nov 10 21:28 subscriptions
drwxrwx---  2 mailnull  mail    512 Nov 13 10:33 tmp
/usr/local/etc/exim>
==========================================

mailnull has system uid=26,
mail has system gid=26.

Kind regards.
Ellad G. Yatsko.