Permissions for shared mail don't work

[Damien Desfontaines]

Good morning,

I'm using dovecot v.2.1.7 on Debian Sid, and the output of dovecot -n
is available here: http://paste.fulltxt.net/C-O

I'm trying to make the mailbox of (system) user "spam" available to
user "ted". I followed these instructions:
    http://wiki2.dovecot.org/SharedMailboxes/Permissions
and it doesn't seem to work. To be more precise:
- I manually (and recursively) changed the permissions of all
  files in ~spam/Mail to 660 (and 770 for the directories);
- I manually (and recursively) changed the group owner of everything
  in ~spam/Mail to "mailperso", where "mailperso" is a group whose
  users are spam and ted;
- I added « mail_access_groups=mailperso » into my dovecot config;
- and I restarted dovecot.

But still, when I send a new email to spam, it appears as being owned
by group "spam" and having permissions set to 600, so I can't access
it with user "ted". I also tried to set the setgid bit for ~spam/Mail,
it didn't change anything, and when I recursively set the setgid for
all subdirectories of ~spam/Mail, it gives new mails the correct group
(mailperso) but not the correct permissions.

Have I missed something, or is this a bug?

Thanks in advance and best regards,

Damien
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