i don't understand why, now that it's easy to write file servers
(compared to unix days), it's necessary to store the mail messages
as actual separate files or directories.  the main problem with
upas/fs i find is that it rewrites the file instead of treating it
as append-only, and it reads the whole thing into memory (in a moderately
bulky format); rather than maintaining a separate index file or files,
and loading as needed.   both the storage and index structure can
then be made suitable for the task.