E-mail is the ultimate open network... everyone's on it. It never works quite right, though. Marc's always calling me from hotels in far off places, after finding that his outbound SMTP connections have been blocked. Martin's mail is currently bouncing, which perhaps has something to do with his server not responding.
I've got a fairly elaborate personal e-mail setup: two mail servers in different datacenters, so a whole server can die and I don't have to care (about mail, at least). It all gets downloaded by POP to a Linux box at home, which serves it out to several clients (two machines, one of which is dual boot). The big FAIL happens when I'm away from home. I sync Thunderbird then flip a switch that points all mail at my fastmail.fm account, which I then have to re-file when I get home as fastmail.fm doesn't know about all the filter rules in the POP downloader.
I could just host all my mail on fastmail.fm, but the server's in New York, which makes it fairly slow for me here in New Zealand. gmail would be nice if it did IMAP, but its folderless model probably wouldn't play well with IMAP so I don't expect that to happen any time soon.
What I'd like is an IMAP server that replicates properly, so I could run a copy on each of my servers, one on a home server, and one on my laptop. Then my mail would just flow around and sync to the relevant place whenever I'm online, and there'd always be a backup. It looks like Cyrus has replication, but it sounds pretty 'bleeding edge' still.
Maybe CouchDB is the answer? Mail is textbook document-centric data. The replication is just what I want. Each folder would have a view, so it should be quick to page through. Anyone want to implement IMAP on CouchDB?