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+Shared Mailboxes in Dovecot Cluster
+===================================
+
+As mentioned in <Director.txt>, you can't have multiple servers accessing the
+same user at the same time or it will lead into trouble. This becomes
+problematic with shared mailboxes, because two users who are sharing a folder
+may run in different servers. The solution here is to access the shared folders
+via IMAP protocol, which passes through the Dovecot proxies/directors so the
+actual filesystem access is done only by one server.
+
+There are a couple of things still missing for this kind of use case:
+
+ * imapc_* settings are global. You can't have two different namespaces with
+   different imapc settings yet.
+ * The imapc code doesn't support many IMAP features. Most importantly SEARCH
+   isn't supported, which may result in lower performance.
+
+Setting up user-shared folders
+------------------------------
+
+You'll need to setup master user logins to work for all the users. The logged
+in user becomes the master user. This way the ACLs are applied correctly.
+
+---%<-------------------------------------------------------------------------
+namespace {
+ type = shared
+ prefix = shared/%%u/
+ location = imapc:~/shared/%%u/ # cache for shared indexes
+}
+imapc_host = director-ip
+imapc_master_user = %u
+#imapc_user = # leave this empty. It'll be automatically filled with the
+destination username.
+imapc_password = master-secret
+
+plugin {
+  acl_shared_dict = fs:posix:prefix=/nfs/shared-acls/
+}
+---%<-------------------------------------------------------------------------
+
+The shared dictionary needs to be accessible from all the backends. The
+possibilities for it are:
+
+ * file: A single shared file in filesystem. This becomes a performance
+   bottleneck easily if there are many users sharing folders.
+ * fs posix: Shared directory in filesystem. This will create many small files
+   to the filesystem.
+ * sql: Shared SQL server
+ * Any other <shared dictionary> [Dictionary.txt]
+
+(This file was created from the wiki on 2019-06-19 12:42)