bug#6574: 24.0.50; Rmail 23 uses a broken mailbox format (mboxo) instead of a sane one like mboxrd

[Mark Lillibridge]

    There is a family of incompatible mbox formats for storing mail; see
http://homepage.ntlworld.com./jonathan.deboynepollard/FGA/mail-mbox-formats.html
for all the details.

    Examining unrmail.el from Gnu emacs 24.0.50.1 (lines 228-231):

            ;; ``Quote'' "\nFrom " as "\n>From "
            ;;  (note that this isn't really quoting, as there is no requirement
            ;;   that "\n[>]+From " be quoted in the same transparent way.)

clearly shows that Rmail 23 is using the mboxo format.  

    Unfortunately, this is known to be a bad format because it
irreversibly alters messages.  I strongly recommend switching to a
format like mboxrd, which does not have this problem.

(In particular, any line in a message body starting with "From " is
changed to ">From " in a nonreversible manner; this will screw up MIME
attachments, among other things, with nonzero probability.)

- Mark
PS, the documentation needs to explain which mbox format is used, rather
than saying "the standard mbox format", of which there is no such thing.