Dovecot permission denied errors on NFS after upgrade to 2.2.17

[Claudio Corvino]

Hi everyone,

we just upgraded our mail server from Debian 8 to Debian 9, so our 
dovecot packages just got upgraded from version 2.2.13 to 2.2.17.

Now we have a lot of errors in our dovecot.log about permission denied 
(our Mailboxes are on NFS remote server since years without problems) 
like these:

Jul 13 12:39:23 Error: imap(XXXXXXXXX): 
open(/mnt/mail-storage/XXXXXXXXX/Maildir/cur/1594378191.M653755P26498.ganimede,S=12716,W=12984:2,S) 
failed: Permission denied (euid=501(vmail) egid=501(vmail) missing +r 
perm: 
/mnt/mail-storage/XXXXXXXXX/Maildir/cur/1594378191.M653755P26498.ganimede,S=12716,W=12984:2,S 
stat(/mnt/mail-storage/XXXXXXXXX/Maildir/cur/1594378191.M653755P26498.ganimede,S=12716,W=12984:2,S) 
failed: Permission denied)

For some user this is not a problem, for some other user this blocks 
their mail client (Thunderbird).

We use vmail user for running Dovecot and I can't find a permission 
problem on the path indicated by the mail error, user vmail can read and 
write and uid and gid seems to be correct.

Permissions on

/mnt/mail-storage

was

drwx------ 94 vmail vmail 4096 ago 29  2019 mail-storage

I just changed to

drwxr-xr-x 94 root root 4096 ago 29  2019 mail-storage

but nothing has changed.

Every directory and sub-dir under

/mnt/mail-storage

is assigned to vmail:vmail with

drwx------

permission set.

If try to stat on

/mnt/mail-storage/XXXXXXXXX/Maildir/cur/1594378191.M653755P26498.ganimede,S=12716,W=12984:2,S

I get permission denied.

We use LMTP and Postfix to deliver mail to mailbox.

mail_debug=yes already enabled; mail_fsync is set to never (should I 
change to always?).

Please could you give us help on the matter as I don't know where to 
look further.

Thanks

Claudio


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