Convert MH mail folders to MBOX files, which are used by Mozilla Thunderbird.

mh2mbox.sh

#!/bin/bash
#
# mh2mbox.sh
# By Eric Lathrop <eric@ericlathrop.com>
#
# Convert MH mail folders to MBOX files
# Useful for switching to Mozilla Thunderbird
#
# Copy this script to ~/Mail/ and execute.
#
# Requires the "packf" command from the nmh package in Ubuntu

DEST="mbox"
# Note: in Ubuntu, packf gets installed under /usr/bin/mh/ so it's not normally in the $PATH
PACKF="/usr/bin/mh/packf"

(IFS='
'
for DIR in `find . -type d`; do
	if [ "$DIR" = "." ]; then
		continue
	fi
	if [ "$DIR" = "./$DEST" ]; then
		continue
	fi

	CONVDIR="."
	if [ `dirname $DIR` !=  "." ]; then
		CONVDIR=`dirname "$DIR" | sed -e "s/\.\///" | sed -e "s/\//.sbd\//g"`'.sbd'
	fi
	mkdir -p "$DEST/$CONVDIR"

	MAILBOX=`basename $DIR`
	MBOXPATH="$DEST/$CONVDIR/$MAILBOX"

	# create an empty file in case there aren't any messages
	# this fixes a thunderbird problem where it won't show subfolders
	# for a folder that doesn't have a matching file
	touch $MBOXPATH

	yes | $PACKF +"$DIR" -mbox -file $MBOXPATH
done
)

Updated as according to suggestion at: https://gist.github.com/ericlathrop/4982676#gistcomment-2222576