I am wondering if there is solution (we currently use Dovecot but another product is ok too), that would allow to setup a second Imap server (or proxy) that would work efficiently over slow links.
An existing email base (over 2TB) from the original mail server will not have to be sync completely over the continents but instead only email headers or some relevant metadata (using custom mailbox format or a metadata file) will be synced.
When new mail arrives at either mail server it will be synced to the other (using whatever tools relevant, e.g. dsync for Dovecot).
Connected via Imap to the second server, if a user clicks on an email that was completely synced (i.e. a new mail) then it will just load as usual. If a user however clicks on an older mail for which only header exists, the secondary mail server will download the rest of the message from the original mail server instead of showing empty message or an error.
Does such solution exist?