Maildir: ACLs/Unix perms and unable to see content of specific mailbox

[Olaf Marzocchi]

Dear Dovecot users, hello.
I will merge two issues I have into a single email because they may be 
related.

I used dovecot on a OmniOS server since 2014 (currently OmniOS r151014) 
with the following configuration (it shows 2.2.18 because I recently 
updated dovecot, skipping only the PostgreSQL plugin):

# 2.2.18: /etc/dovecot/dovecot.conf
# OS: SunOS 5.11 i86pc  zfs
mail_location = maildir:/tank/home/%u/Maildir
mail_privileged_group = mail
namespace inbox {
   inbox = yes
   location =
   mailbox Drafts {
     special_use = \Drafts
   }
   mailbox Junk {
     special_use = \Junk
   }
   mailbox Sent {
     special_use = \Sent
   }
   mailbox "Sent Messages" {
     special_use = \Sent
   }
   mailbox Trash {
     special_use = \Trash
   }
   prefix =
}
passdb {
   driver = pam
}
protocols = imap
ssl = required
ssl_cert = </etc/dovecot/certs/dovecot.pem
ssl_key = </etc/dovecot/private/dovecot.pem
userdb {
   driver = passwd
}

You can see that I set the Maildir folder inside the shared home folders 
of my server (it is only one user, anyway).
It always worked perfectly, but one-two months ago I changed the 
permissions of my whole home folder, recursively, to add proper ACLs. I 
needed them because the clients started using illumos kernel SMB 
(relying on ACLs) instead of Netatalk/AFP (relying on Unix perms only).
I didn't realise I applied the ACLs also to the Maildir folder.

Dovecot worked for several weeks fine, I noticed the issue only 
yesterday when a mailbox (see below) appeared in Thunderbird completely 
empty even if the "cur" subfolder on the server still contains all the 
mails.

Dovecot was throwing some errors like:

dovecot: [ID 583609 mail.error] imap(olaf): Error: 
rename(/tank/home/olaf/Maildir/.&A6k- Mailing 
Lists.Log/dovecot.index.cache) failed: Permission denied (euid=501(olaf) 
egid=501(olaf) UNIX perms appear ok (ACL/MAC wrong?))
dovecot: [ID 583609 mail.error] imap(olaf): Error: 
rename(/tank/home/olaf/Maildir/.&A6k- Mailing 
Lists.Log/dovecot.index.tmp, /tank/home/olaf/Maildir/.&A6k- Mailing 
Lists.Log/dovecot.index) failed: Permission denied
dovecot: [ID 583609 mail.error] imap(olaf): Error: 
unlink(/tank/home/olaf/Maildir/subscriptions.lock) failed: Permission denied
dovecot: [ID 583609 mail.error] imap(olaf): Error: 
rename(/tank/home/olaf/Maildir/subscriptions.lock, 
/tank/home/olaf/Maildir/subscriptions) failed: Permission denied

I will post here the current permissions of the folder containing 
Maildir, of the Maildir itself, of its contents, and of the folder that 
appears empty when browsed with a client (Thunderbird).

/tank/home/olaf $ ls -lV ..
drwx------+ 16 olaf     olaf          17 Sep 19 01:52 olaf
               user:olaf:rwxpdDaARWcCos:fd-----:allow
        group:2147483648:rwxpdDaARWcCos:fd-----:allow
               everyone@:rwxpdDaARWcCos:fd-----:deny

/tank/home/olaf $ ls -lV
drwxrwx--- 348 olaf     olaf         359 Sep 19 01:51 Maildir
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow

/tank/home/olaf $ ls -lV Maildir/
drwxrwx---   2 olaf     olaf           2 Jan 30  2014 cur
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow
-rwxrwx---   1 olaf     olaf          21 Jan 30  2014 dovecot-keywords
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow
(ALL THE SAME PERMISSIONS FOR THE OTHER FILES EXCEPT...)
-rwxrwx---   1 olaf     olaf       13735 Jan 24  2015 subscriptions
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow
-rw-rw----   1 olaf     olaf       13709 Sep 19 01:51 subscriptions.lock
                  owner@:rw-p--aARWcCos:-------:allow
                  group@:rw-p--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow

The folder that appears empty:

/tank/home/olaf $ ls -lV Maildir/.Generiche/
total 513
drwxrwx---   2 olaf     olaf         949 Sep 18 01:42 cur
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow
-rwxrwx---   1 olaf     olaf          46 May 18  2014 dovecot-keywords
                  owner@:rwxp--aARWcCos:-------:allow
                  group@:rwxp--a-R-c--s:-------:allow
               everyone@:------a-R-c--s:-------:allow
(ALL THE SAME PERMISSIONS FOR THE OTHER FILES)


I really hope you will have the time to help me because I already 
applied the permissions recursively and I removed the ACLs, almost as it 
was before my mistake.
I specified "almost" because originally (I checked the backups) the 
Maildir folder had an ACL that gave access permissions also to the group 
"mail":

drwxrwx---+349 olaf     olaf         359 Feb 16  2014 Maildir
              group:mail:rwxpdDaARWcCos:fd-----:allow
                  owner@:rwxpdDaARWcCos:fd----I:allow
                  group@:rwxpdDaARWcCos:fd----I:allow
               everyone@:rwxpdDaARWcCos:fd----I:deny

Yesterday I haven't replicated it because from the documentation I 
understood it was not necessary.

My questions, in short:
- what are the permissions I need to give to the Maildir folder? I 
understood from the documentation it's 700, with my user/group (the one 
of the user accessing the mail). What about ACLs? and what about group 
"mail"?
- the (only!) subfolder which appears empty in Thunderbird, may it 
depend on the permissions? maybe due to them the index was not updated 
and UIDs don't match. If after applying the correct permissions I still 
cannot see its contents, is there a way to recover the mails? the files 
are all still there.

Sorry for the long email, but after several tries yesterday I exhausted 
my ideas.

Regards,
Olaf