For storing mailboxes in index format, the simplest approach is the
one used by MH:  one message per file, and a mailbox is a directory.

For storing messages in a single file, here is a simple scheme that
will remove all ambiguity.  It's a combination of old and new
strategies.

1. (old) 'From ...' (standard pattern) at beginning of line (BOL)
   begins a message
2. (old) 'From ' at BOL, when part of the message body, is
   converted to '>From ' before the message is added into
   a mailbox.
3. (new) '>From ', '>>From ', '>>>From ', etc., at BOL, when part of the
   message body, are escaped by prepending on '>' before the message
   is added into a mailbox.
4. (new) The mail agent always strips out one '>' from any instance of
   '>From ', '>>From ', '>>>From ', etc. at BOL, before showing the message
   to the user or moving it from a mailbox into any non-mailbox location.

Ok, look at the advantages of this scheme.

1. A mail reader using the above scheme is 100% compatible with
existing mailbox formats.

2. Said mail reader will correctly show 'From ' at BOL in a message
body, by stripping out the superfluous '>' that is added by existing
mail delivery agents.

3. If said mail reader finds occurrences of '>>From ', '>>>From ',
etc., at BOL in a message body, it may unnecessarily strip out one '>'.
In practice this is unlikely to cause problems.

4. Mail readers and delivery agents can be incrementally revised to
use this scheme.
--
Rahul Dhesi <dh...@rahul.net>
"please ignore Dhesi" -- Mark Crispin <m...@CAC.Washington.EDU>