I'm confused now. Does the CSSU include the OfflineIMAP program? I thought the "Offline IMAP" option in modest relates to activating the e-mail caching (provided by Tinymail). Basically this involves two patches (one in modest, one in tinymail). But then I see these mentions of offlineimap.org, which is a completely different thing, as (1) is a separate program, (2) needs a client with Maildir support, (3) which modest doesn't have, so it requires (4) a local IMAP server. None of that is AFAIK included with the CSSU. At least I have seen no mention of it. So please somebody clarify this. Otherwise the "documentation" (at least the wiki) will be spreading misinformation.
In Tinymail we handle two types of "server accounts", that are important in !Modest: Store accounts: represent storages of messages. !Modest uses !Tinymail implementations for !IMAP, !POP, and !Maildir storage. The storages keep references to the folders where messages are stored.