#!/usr/bin/perl
use Mail::Mbox::MessageParser;
use Email::MIME;
use Encode;

my $infile = shift @ARGV;

Mail::Mbox::MessageParser::SETUP_CACHE(
    {
'file_name' => 'mbox.cache'
});

my $folder_reader = new Mail::Mbox::MessageParser({
'file_name' => $infile,
'enable_grep' => 1,
 });
 die $folder_reader unless ref $folder_reader;

 # This is the main loop. It's executed once for each email
 while(!$folder_reader->end_of_file()){
 my $rawemail = $folder_reader->read_next_email();
 my $email = Email::MIME->new($rawemail);

    $email->body_set("New Body Text");

      print $email->as_string