[Hampshire] Kmail

Does anyone use Kmail? If so can you explain to me what "Servside
subscription" and "Local subscription" are on an IMAP account? Despite
much googling I still haven't found a decent explanation. I know that
it's possible to cache email from an IMAP account locally, for reading
when disconnected and I presume one of the subscriptions represents
that. I just don't know which, and what the other is for.

Thanks,
Leo