受注詳細のメール通知からメール送信した際に処理を追加する

$event = new EventArgs(
[
'form' => $form,
'Order' => $Order,
'MailTemplate' => $MailTemplate,
'MailHistory' => $MailHistory,
],$request);
$this->eventDispatcher->dispatch(EccubeEvents::ADMIN_ORDER_MAIL_INDEX_COMPLETE, $event);

<?php
declare(strict_types=1);
namespace Customize\EventListener\Admin;

use Doctrine\ORM\EntityManagerInterface;
use Eccube\Controller\AbstractController;
use Eccube\Entity\Order;
use Eccube\Entity\Shipping;
use Eccube\Repository\ShippingRepository;
use Eccube\Service\PurchaseFlow\PurchaseContext;
use Eccube\Service\PurchaseFlow\PurchaseFlow;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Eccube\Event\EccubeEvents;
use Eccube\Event\EventArgs;

/** 受注詳細のメール送信完了後に処理を追加する
 */
class OrderMailIndexCompleteListener extends AbstractController implements EventSubscriberInterface
{
    /**
     * @var EntityManagerInterface
     */
    protected $entityManager;

    /**
     * OrderEditIndexCompleteListener constructor.
     *
     * @param  EntityManagerInterface  $entityManager
     */

    /**
     * @var PurchaseFlow
     */
    protected $purchaseFlow;

    /**
     * @var ShippingRepository
     */
    protected $shippingRepository;

    public function __construct(
        EntityManagerInterface $entityManager,
        PurchaseFlow $purchaseFlow,
        ShippingRepository $shippingRepository
    ) {
        $this->entityManager      = $entityManager;
        $this->purchaseFlow       = $purchaseFlow;
        $this->shippingRepository = $shippingRepository;
    }

    public static function getSubscribedEvents(): array
    {
        return [
            EccubeEvents::ADMIN_ORDER_MAIL_INDEX_COMPLETE => 'onAdminOrderMailIndexComplete',
        ];
    }


    /**
     * メール通知 受注管理から出荷メールを送った際の処理
     *
     * @param  EventArgs  $event
     *
     * @throws \Exception
     */
    public function onAdminOrderMailIndexComplete(EventArgs $event)
    {
        /** @var Order $Order */
        $Order         = $event->getArgument('Order');
        $orderMailType = $event->getArgument('MailTemplate');

        //出荷メールの場合のみ実行
        if ($orderMailType->getId() === 8) {

            $Shippings = $Order->getShippings();

            foreach ($Shippings as $Shipping) {
                $this->entityManager->persist($Shipping);
                $Shipping->setMailSendDate(new \DateTime());
                $this->shippingRepository->save($Shipping);
            }
            $this->entityManager->flush();

            $this->addInfo('「対応状況のステータスを配送手続き完了にしてください。」', 'admin');
        }

    }

}