This may or may not be considered desirable by
those with slower computers, but I'd like to see
mbox files gzipped to save HD space.

On my largest mboxes, gzip roughly yields a 3:1
compression ratio. This begins to make a
difference when dealing with thousands of messages.

If this were implemented, I would think that you'd
want to decompress after displaying the headers
from the ev-summary on open, and then recompress
either on exit or upon completion of the
decompression step on another folder.

Not too sure how much of a performance hit this
would create on older systems, but the compression
takes about 1.25 seconds on a 11mb file,
decompression takes 0.25s on a 1.2 GHz Athlon.