Postfix/Dovecot permissions for new mailboxes

Hello,

the wiki page describe that permission should copied from root mail directory https://wiki2.dovecot.org/SharedMailboxes/Permissions

The permissions for the root mail directory are set to 2770: drwxrws--- 36 root mail 4096 Apr 15 02:30 /var/spool/mail/

But newly created mailboxes get following permissions: drwx--S--- 5 newuser mail 4096 Apr 23 19:31 /var/spool/mail/newuser/

In /etc/dovecot/conf.d/10-mail.conf follow options are set: mail_gid = mail mail_privileged_group = mail mail_access_groups = mail

I'm missing something to get right group permissions for new mailboxes?