From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed,  8 Apr 1998 13:08:14 -0400
From: Russ Cox rsc@plan9.bell-labs.com
Subject: [9fans] allowing space (ASCII 0x20) in file names
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intro(5) says "Plan 9 names may contain any printable character
(that is, any character outside hexadecimal 00-1F and 80-9F) except
slash and blank", so yes it looks like the idea is to disallow
unprintables.

i don't know the official reasons that space isn't allowed,
but in general file names with spaces (which you have to deal
with in Unix and Windows) are a pain for oodles of reasons.  the most
noticeable one is that it messes up scripts and the like:
ls -l | awk '{print $10}' is no longer guaranteed to give 
you filenames.  that's just the tip of the iceberg.
"B <echo *.c" in sam would fail.  there is much more.
not having spaces in the filenames in plan9 is a wonderful
blessing.

just my 2¢, but i'd rather have ms-dos filenames than have spaces.
come to think of it, i think i'd rather have ms-dos filenames than
have imap.  use import and edmail.  or pop3 | sendmail.