#!/bin/bash
for mbox ; do
    num=0
    fnum=head
    while read line ; do
         case "$line" in
         'From '*)
             fnum=$(echo 0000$num|sed -e 's/.*\(....\)$/\1/')
             num=$(( $num + 1 ))
             ;;
         esac
         echo "$line" >> "${file}.${fnum}"
    done < "$mbox"
done