【dovecot】ThunderbirdからDovecotへ接続した際にPermission Deniedと表示されてしまう

Aug 25 00:11:46 mail1 dovecot: imap(cent): Error: fchown(/home/cent/mail
/.imap/INBOX, group=12(mail)) failed: Operation not permitted
(egid=1000(cent), group based on /var/mail/cent - see
http://wiki2.dovecot.org/Errors/ChgrpNoPerm)
chmod 0600 /var/mail/*
https://server-setting.info/centos/dovecot-fchmod-error.html