$mailuserlist=DB::table('table')
            ->join('some_table')
            ->select('some_thing')
            ->where('somecondition'))->get();

Mail::queue('mail_template', $data, function($message) use ($mailuserlist)
{
      $message->from('test@desto.co.in', 'Mail Notification');
      foreach ($mailuserlist as $value) {
            $message->to($value['email'],$value['firstname'].' '.$value['lastname']);
    }
    $message->subject('Testing mail');
});

$mailuserlist=DB::table('table')
        ->join('some_table')
        ->select('some_thing')
        ->where('somecondition'))->get();

foreach ($mailuserlist as $mailuser) {
    Mail::queue('mail_template', $data, function($message) use ($mailuser) {
        $message
          ->from('test@desto.co.in', 'Mail Notification')
          ->to($mailuser['email'],
            $mailuser['firstname'].' '.$mailuser['lastname'])
          ->subject('Testing mail');
    });
}