[Dovecot] Per-user seen flags for public read-only mailboxes

[Guido Berhoerster]

Hi,

I have some trouble getting per-user SEEN-flags to work with
read-only mailboxes in a public namespace. Basically, I'm
following the wiki at
http://wiki2.dovecot.org/SharedMailboxes/Public#Maildir:_Per-user_.2BAFw-Seen_flag
and the relevant configuration is as follows:

namespace {
  inbox = yes
  location =
  prefix =
  separator = /
  type = private
}
namespace {
  location = maildir:/srv/mail/public:LAYOUT=fs:INDEX=~/public
  prefix = Public/
  separator = /
  subscriptions = no
  type = public
}
plugin {
  acl = vfile
...
}
protocol imap {
  mail_plugins = " acl quota trash zlib autocreate imap_acl imap_quota imap_zlib"
}

I have a virtual-user setup with static userdb and there is no
permissions problem since everything is created through dovecot:

mail_gid = vmail
mail_location = mdbox:~/mdbox
mail_uid = vmail
[...]
userdb {
  args = uid=vmail gid=vmail home=/srv/mail/virtual/%n
  driver = static
}

The content of /srv/mail/public/dovecot-acl (and the one of all
mailboxes below it) is:

owner lrwstipekxa
authenticated lr

Users can access all mailboxes in the Public/ namespace and read
the messages and I can see that dovecot.index.cache and
dovecot.index.log are created under ~/public, however setting the
SEEN flag for a message is ignored since the mailbox is
read-only. Changing the ACL from

authenticated lr

to

authenticated lrs

allows user to set the SEEN flag, but globally on the actual
mailbox.
How can I get per-user SEEN flags to work? The Dovecot version is
2.0.9.

Thanks,
-- 
Guido Berhoerster