sub add {
    my ($hashref, $to, $subject, $file_name, $from, $last_dir) = @_;

    $hashref -> {$to} ||= { };
    $hashref -> {$to} {$subject} ||= [ ];
    push @{$hashref -> {$to} {$subject}} =>
          {$file_name => {path => $last_dir,
                          from => $from}};
}