[Dovecot] Manual thread breaking from Thunderbird

[rosenfield.albert at gmail.com]

> The configured virtual mailbox would look exactly
> like a normal mailbox  to the client.

The advantage being that Dovecot would index messages in all physical
folders for super-fast access when asking via IMAP for messages
relating to a specific thread-id.  (Hope I got this right.)

In case I wanted to modify the MUA to support better threading and
tags/labels, is that enough?  Can I simply tell Dovecot via IMAP to
create a new virtual folder that aggregates virtual messages from all
the other folders and it will start indexing them for thread-locality?

(Would be great, because it's always easier when you only have to
change either the MUA or the "post office" side of things.)

Is it possible to ask Dovecot via IMAP to look for other things in the
virtual folder, for example all items with the flag "huey lewis"
applied?  Is this sort of query fast / indexed?