my $manager = Mail::Box::Manager->new;
my $folder  = $manager->open( folder => $ENV{MAIL} );
foreach my $message ( $folder->messages ) {
  next if $message->label( 'seen' );
  my $bounce = $message->bounce( To => 'you@somewhere.com' );
  $bounce->send;
  $message->label( 'seen' => 1 );
}
$folder->close;