apt-get install offlineimap, set up a few options, and I now have a(n efficiently syncable) copy of my mail on my laptop.
Now to figure out the sending half.
[from Offline Mail in Linux]
Of course, it doesn't work if I read my mail spool locally. So my options are either to use imap even when I'm ssh'd into the remote machine (ew) or... nothing, as far as I can tell.