Shared Mailboxes in Dovecot Cluster
As mentioned in Director, 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