[Dovecot] Replication via sneakernet

[David Bishop]

Is there a way to get a running transaction log from a Dovecot instance to
synchronize (and I use that word very, very loosely) multiple instances
that don't share a network?

Why I would want to do such a thing: I have a couple way stations along a
long, winding road through very hilly country, and at each of these
stations, I have a few people (and many, many more at one end of the road).
Which people are where varies from hour to hour (but they're all members of
a known, larger, group of people with accounts). It would be helpful to get
communication (however limited) along this road (and establishing direct
communication, either through radio or landline, is not feasible within the
budget constraints I have), and it is possible to store a complete copy of
the mail spool to a small box at each station (the total mail spool over
the period I care about is in the tens of megs).

There are trams shuttling back and forth along this road (stopping at each
station), and adding a small box (such as a weatherproofed Raspberry Pi
with a wifi dongle) to transport files up and down the road is pretty
simple. Doing incremental copies of the mail spool is also simple, keeping
track of files that get moved or deleted is a bit harder (but still not
that bad), but I have no idea how hard it is to track what messages have
been seen, especially for the shared folders (which we use instead of
mailing lists).

I realize this is not a "normal" use of Dovecot, but given this, does
anyone who knows the software (and how it keeps track of messages) better
have suggestions on how to approach the problem?