Create Public/Shared Mailbox on OS X Server 10.9.5 with Dovecot 2.2.5

how can I create a Public/Shared Mailbox on OS X Server? This Mailbox should be available to all authenticated Users on my network and should be automatically subscribed into a folder "Public" in the Mailbox folder structure. The folder structure in the IMAP inbox should look similar to this:

Inbox
  |- User-Folder1
  |- User-Folder2
Send
Deleted
Public
  |- Public-Mailbox-1
  |- Public-Mailbox-2
  |- Public-Mailbox-3

What I have done so far:

• I created a User in the LDAP-Directory with an email address "accounts@domain.de" <- Only as workaround to get a mailbox

• I modified this file: /Library/Server/Mail/Config/dovecot/conf.d/15-mailboxes.conf and added this lines at the end:

  namespace {
      type = public
      separator = .
      prefix = Public.
      location = maildir:/Volumes/Data/Library/Server/Mail/Data/mail/users/accounts/
      subscriptions = yes
      list = yes
      mailbox Public {
              auto = subscribe
      }
  }
  

When I login into my IMAP account on the server via webmail (roundcube) I can see the folder in the IMAP "Manage folders" but I can not subscribe to it. Has anyone an idea how I can get this?

Is it also possible not to create an LDAP User, to get an Mailbox for some special email addresses (accounts, info)?

Thanks Oliver

Version Numbers: OS X 10.9.5 Server App 3.2.1 (clean install no update) Postfix: postconf -d | grep mail_version mail_version = 2.9.4 Dovecot: sudo dovecotd --version 2.2.5

Info: Also posted here: https://discussions.apple.com/message/26829189