On Wed Jan 17 2018 15:56:39 GMT-0500 (Eastern Standard Time), Joseph Tam <jtam.home@gmail.com> wrote:

Thanks. How does this manifests itself: the client gets an inconsistent view of the outgoing mailbox that depends on which mailbox the client is using, or the optimization is broken and dovecot keeps having to (re)read the mailbox to acquire the IMAP STATUS?

The way I think this should work is simple...

If the Client doesn't request one of the pre-defined 'aliases' for a special use folder, then it simply does what it does now - uses what it wants (creates it if it doesn't exist).

As far as I can tell, this would require dovecot to add some 'smarts' with respect to virtual folders, and be able to create these on the fly for clients, as virtual folders is how I think these special-use aliases should be presented to the client, unless someone has a better idea.

So, for example, if a client asks for a special use folder that did not use to be pre-defined (Admin added it sometime after the client connected before), it moves any emails currently residing in the real version of what will be the new 'alias' (virtual) folder to the alias target (the real special use folder on the filesystem), deletes the real version, then creates and subscribes to the new virtual folder.

As I said, properly coded, this could be painless and mostly invisible to the client.