Send a test mail from the admin and log why delivery failed

Form submissions marked as not sent gave no reason: the transport
exception was swallowed. Every send now goes through MailCheck, which
logs the server's answer and a hint in German to var/log/mail.log
(server lines only, no credentials). The system screen shows the mail
route, sends a test mail to any address and lists recent attempts
(ADR 121).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Controller/SystemController.php

@@ -11,6 +11,7 @@ use App\Ops\Backup;
 use App\Ops\Environment;
 use App\Ops\HttpsRedirect;
 use App\Ops\Installation;
+use App\Ops\MailCheck;
 use App\Ops\OriginCheck;
 use App\Ops\SitePackage;
 use App\Ops\Updater;
@@ -19,6 +20,8 @@ use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Component\Mime\Address;
+use Symfony\Component\Mime\Email;
 use Symfony\Component\Routing\Attribute\Route;
 
 /**
@@ -30,7 +33,7 @@ use Symfony\Component\Routing\Attribute\Route;
  */
 final class SystemController extends AbstractController
 {
-    public function __construct(private Updater $updater, private Backup $backup, private ArchiveUpdate $archive, private Installation $installation, private string $adminPath, private string $databaseUrl, private string $mediaDirectory, private string $projectDir, private string $siteOrigin, private OriginCheck $originCheck, private HttpKernelInterface $kernel, private PageRepository $pages, private SiteSettings $settings, private SitePackage $packages, private HttpsRedirect $https)
+    public function __construct(private Updater $updater, private Backup $backup, private ArchiveUpdate $archive, private Installation $installation, private string $adminPath, private string $databaseUrl, private string $mediaDirectory, private string $projectDir, private string $siteOrigin, private OriginCheck $originCheck, private HttpKernelInterface $kernel, private PageRepository $pages, private SiteSettings $settings, private SitePackage $packages, private HttpsRedirect $https, private MailCheck $mail)
     {
     }
 
@@ -71,6 +74,9 @@ final class SystemController extends AbstractController
             // HTTPS erzwingen und HSTS (ADR 120): der Stand in public/.htaccess.
             'https' => $this->https->state(),
             'secure' => $request->isSecure(),
+            // E-Mail-Versand (ADR 121): Weg ohne Passwort, Testmail, die letzten Versuche.
+            'mail' => $this->mailFacts(),
+            'mailResult' => $request->getSession()->remove('mail_result'),
         ]);
     }
 
@@ -520,6 +526,51 @@ final class SystemController extends AbstractController
         return $this->back($result['message'], $result['ok'] ? 'success' : 'error');
     }
 
+    /**
+     * Eine Testmail an eine frei eingetragene Adresse (ADR 121). Das Ergebnis - Meldung, Hinweis,
+     * Antworten des Servers - steht danach auf der Seite und in var/log/mail.log.
+     */
+    #[Route('/%kant.admin_path%/system/testmail', name: 'admin_system_testmail', methods: ['POST'])]
+    public function testMail(Request $request): Response
+    {
+        $this->denyAccessUnlessGranted('ROLE_ADMIN');
+        if (!$this->isCsrfTokenValid('system', $request->request->getString('_csrf_token'))) {
+            return $this->back('Deine Sitzung ist abgelaufen. Bitte melde dich erneut an.');
+        }
+        $an = trim($request->request->getString('to'));
+        $von = trim($request->request->getString('from')) ?: $an;
+        foreach ([$an, $von] as $adresse) {
+            if (false === filter_var($adresse, FILTER_VALIDATE_EMAIL)) {
+                return $this->back(sprintf('„%s“ ist keine gültige E-Mail-Adresse.', mb_substr($adresse, 0, 100)));
+            }
+        }
+        $website = rtrim($this->siteOrigin, '/') ?: $request->getSchemeAndHttpHost();
+        $email = (new Email())
+            ->from(new Address($von))
+            ->to(new Address($an))
+            ->subject('Testmail von '.(parse_url($website, PHP_URL_HOST) ?: $website))
+            ->text("Diese Testmail kommt aus der Verwaltung von {$website} (System → E-Mail-Versand).
+
+Wenn sie angekommen ist, funktioniert der Versand der Formulare auf demselben Weg.
+");
+        $request->getSession()->set('mail_result', ['an' => $an, 'von' => $von] + $this->mail->send($email, 'Testmail'));
+
+        return $this->redirect($this->generateUrl('admin_system').'#mail');
+    }
+
+    /** @return array<string, mixed> */
+    private function mailFacts(): array
+    {
+        $route = $this->mail->route();
+
+        return $route + [
+            'quelle' => $this->environmentSource('MAILER_DSN'),
+            // Wer sich mit einer Adresse anmeldet, versendet meist auch nur unter ihr.
+            'absender' => false !== filter_var($route['benutzer'], FILTER_VALIDATE_EMAIL) ? $route['benutzer'] : '',
+            'protokoll' => $this->mail->recent(),
+        ];
+    }
+
     /** Die Gegenstelle zur Prüfung oben: öffentlich, und sie verrät nichts als diese Kennung. */
     #[Route(OriginCheck::PATH, name: 'site_origin_probe', methods: ['GET'], priority: 10)]
     public function originProbe(): Response