public function sendActivationMail($id = null)
    {
        $user = $this->Users->get($id, [
            'contain' => []
        ]);

        $user->set('active', false);
        $user->set('activation_key', $this->Users->generateActivationKey());

        if ($this->Users->save($user)) {
            $this->EmailListener->activation($user);
            $this->Flash->success(__('The e-mail has been sent.'));
            return $this->redirect($this->referer());
        } else {
            $this->Flash->error(__('The e-mail could not be sent. Please, try again.'));
        }
    }