Shared mailboxes and public namespaces

Three namespace types: private (each user's own), shared (other users' mailboxes), public (everyone sees the same folders).

Public namespace in 10-mail.conf:

namespace public {
  type = public
  separator = /
  prefix = Public/
  location = maildir:/var/mail/vhosts/public:INDEXPVT=~/public-index
  list = yes
  subscriptions = no
}

Shared namespace (folders other users have ACL'd to you):

namespace {
  type = shared
  separator = /
  prefix = Shared/%%u/
  location = maildir:%%h/Maildir:INDEX=~/shared/%%u
  subscriptions = no
  list = children
}

Grant access via the ACL plugin (90-acl.conf + dovecot-acl file in the source mailbox):

user=bob@example.com lrws

Bob now sees the folder under Shared/alice@example.com/ in his client.

Common use: a support@ mailbox shared with the whole team — replies thread cleanly because everyone reads/writes the same store.