Issue #110: update book tutorial

Signed-off-by: horea <horea@rospace.com>

Author: Howriq

docs/book/v6/extended-features/email.md

@@ -1,11 +1,73 @@
 # Email sending and content parsing
 
 In the previous version of Dotkernel API we have been using the `mezzio/mezzio-twigrenderer` package which added unnecessary complexity to the email sending in our API platform since APIs returns JSON data, not HTML.
-In order to fix this issue, we have come up with a lighter custom solution.
+Besides this, it used two services (`AdminService` and `UserService`) to send emails.
+It was not necessarily wrong, but their job should be only to manage Admin/User accounts.
+
+In order to fix this those problems, we have come up with a lighter custom solution.
 Now each project can prepare the bodies of the emails by using its preferred template renderer.
-`Core\App\MailService` is now decoupled by injecting the pre-rendered email body when calling its methods.
+`Core/src/App/src/Service/MailService` is now decoupled by injecting the pre-rendered email body when calling its methods.
+
+Example from `Core/src/App/src/Service/MailService.php`:
+
+```php
+<?php
+
+declare(strict_types=1);
+
+namespace Core\App\Service;
+
+use Core\App\Message;
+use Core\User\Entity\User;
+use Dot\DependencyInjection\Attribute\Inject;
+use Dot\Log\LoggerInterface;
+use Dot\Mail\Exception\MailException;
+use Symfony\Component\Mailer\Exception\TransportExceptionInterface;
+
+use function sprintf;
+
+class MailService
+{
+    /**
+     * @param array<non-empty-string, mixed> $config
+     */
+    #[Inject(
+        'dot-mail.service.default',
+        'dot-log.default_logger',
+        'config',
+    )]
+    public function __construct(
+        protected \Dot\Mail\Service\MailService $mailService,
+        protected LoggerInterface $logger,
+        private readonly array $config,
+    ) {
+    }
+
+    /**
+     * @throws MailException
+     */
+    public function sendActivationMail(User $user, string $body): bool
+    {
+        if ($user->isActive()) {
+            return false;
+        }
+
+        $this->mailService->getMessage()->addTo($user->getEmail(), $user->getName());
+        $this->mailService->setSubject('Welcome to ' . $this->config['application']['name']);
+        $this->mailService->setBody($body);
+
+        try {
+            return $this->mailService->send()->isValid();
+        } catch (MailException | TransportExceptionInterface $exception) {
+            $this->logger->err($exception->getMessage());
+            throw new MailException(sprintf(Message::MAIL_NOT_SENT_TO, $user->getEmail()));
+        }
+    }
+}
+```
+
+Rending example from `src/User/src/Handler/PostUserResourceHandler.php`:
 
-Example from `src/User/src/Handler/PostUserResourceHandler.php`:
 ```php
 if ($user->isPending()) {
     $this->mailService->sendActivationMail(
@@ -14,8 +76,8 @@ if ($user->isPending()) {
     );
 }
 ```
+
 In this case we are using the `phtml` template from `src/User/src/templates`.
 It has a lighter format compared to `twig`.
 It is then rendered before sending the activation email by our custom renderer from `src/App/src/Template/Rederer.php`.
 The other applications that use the Core structure such as [Dotkernel Admin](https://docs.dotkernel.org/admin-documentation/) use `mezzio/mezzio-twigrenderer` for this purpose.
-