We've recently run in to a situation where we had a fairly large number of legitimate messages bounce due to a misconfigured MTA. Once we fixed the MTA, we needed to get all of those messages back out the door again. It was a job for CPAN.

    

use strict;
use warnings;        
use Mail::Box::Manager;
use Email::MIME;
use Email::Send;

foreach my $mbox (@ARGV) {
    my $mgr = Mail::Box::Manager->new;
    my $folder = $mgr->open(folder => $mbox);
    my $sender = Email::Send->new({mailer => 'SMTP'});
    $sender->mailer_args([Host => 'localhost']);

    foreach my $msg ($folder->messages) {
        PART: foreach my $part ($msg->parts('ALL')) {  
            my $body =  $part->decoded;
            if ($body =~ /This is the mail system at/) {
                next PART;
            } elsif ($part->decoded =~ /Action: failed/) {
                next PART;
            } else {
                my $email = Email::MIME->new(\$part->decoded);
                print "Sending to: " . $email->header("To") . "\n";
                $sender->send($email);
            }
        }
    }
}

The code uses a couple of different modules:

1. Mail::Box::Manager: handles opening a mailbox (in pretty much every common format) and extracting messages.
2. Email::MIME: lets you construct a new email from a MIME encoded message.
3. Email::Send: takes our Email::MIME object and sends it out (in this case, via SMTP, but you can choose your mechanism.)

So should you ever find yourself with a couple thousand erroneously bounced messages, don't fret. ;)