preserve mbox delimiter by default (`-m`)?

[cardi]

Based on RFC 4155, emails in the mbox format are delimited by something like the following (from Wikipedia):

From MAILER-DAEMON Fri Jul  8 12:08:34 2011

decode_email.py works on individual messages, and one person lost some mail because the resulting message did not contain the delimiter—the script requires the -m to be set explicitly.

Thus, can we set the default to always preserve the Mbox-style From?

• Does the Mbox-style From affect messages stored in Maildirs?
• Should we auto-detect whether it's in Mbox-format or not and preserve accordingly?

If -m is used on a message that isn't in Mbox-format, do we add the delimiter? Correspondingly, do we support an option to remove the delimiter in the cleaned message, if one exists? My inclination is to not mess with email message formats any more than necessary.

So the current plan would be to, by default, preserve the Mbox-style From, and -m would no longer do anything (deprecated, but remain there).