diff --git a/UPGRADE.md b/UPGRADE.md
index f0931e17..a09700f2 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -3,7 +3,6 @@
 * The built-in Postmark gateway has been removed.
 * The built-in queue gateway has been removed.
 * The built-in file gateway has been removed.
-* Embedding images in e-mails is not supported anymore.
 * Attachment templates are not supported anymore.
 * The configurable flattening delimiter in the e-mail notification type has been removed.
 * The configurable template in the notification type has been removed.
@@ -17,7 +16,10 @@
   you will have to adjust your workflow. This module has been removed. However, the "Subscribe (Notification Center)"
   now has a second forward page setting. You can use this one in order to have a separate confirmation page.
 * Tokens will not be validated in the back end anymore. Basically because it's totally okay to write something
-  like `##something-not-token-related##` in your message, and you should be able to write this.
+  like `##something_not_token_related##` in your message, and you should be able to write this.
+* Tokens will be normalized! In Contao 5, having a token with e.g. a dash (`##my-token##`) is not supported in `{if`
+  statements anymore. Hence, the Notification Center 2 will normalize this to `##my_token##`. Allowed token names have
+  the same requirement as PHP variables. All invalid characters will be replaced with a `_`.
 * The `filenames` token introduced in 1.7 has been removed. It's a very specific use case which can be provided very easily
   as a third party bundle now (not easily possible before and thus part of the core in 1.7).
 * The `member_*` tokens in the `lost_password` notification type used to contain the raw database values, they are now
diff --git a/composer.json b/composer.json
index 6ddbd2b5..8b30cef7 100644
--- a/composer.json
+++ b/composer.json
@@ -54,9 +54,11 @@
     "require-dev": {
         "contao/manager-plugin": "^2.0",
         "contao/newsletter-bundle": "^5.0",
-        "phpunit/phpunit": "^10.0",
-        "terminal42/contao-build-tools": "dev-main",
-        "contao/test-case": "^4.9"
+        "contao/test-case": "^5.3",
+        "league/flysystem-memory": "^3.25",
+        "phpunit/phpunit": "^9.6",
+        "symfony/expression-language": "^5.4 || ^6.0 || ^7.0",
+        "terminal42/contao-build-tools": "dev-main"
     },
     "suggest": {
         "terminal42/contao-notification-center-pro": "Turn your Notification Center 2 into a pro version and benefit from logs, various testing tools and your own Simple Tokens that can be completely customized with Twig."
diff --git a/config/listeners.php b/config/listeners.php
index 46a099b2..d09a0fdb 100644
--- a/config/listeners.php
+++ b/config/listeners.php
@@ -107,6 +107,7 @@
         ->args([
             service(NotificationCenter::class),
             service(FileUploadNormalizer::class),
+            service(ConfigLoader::class),
         ])
     ;
 
diff --git a/config/services.php b/config/services.php
index 7c55642a..9390a619 100644
--- a/config/services.php
+++ b/config/services.php
@@ -8,6 +8,7 @@
 use Symfony\Contracts\Translation\TranslatorInterface;
 use Terminal42\NotificationCenterBundle\Backend\AutoSuggester;
 use Terminal42\NotificationCenterBundle\BulkyItem\BulkyItemStorage;
+use Terminal42\NotificationCenterBundle\BulkyItem\FileItemFactory;
 use Terminal42\NotificationCenterBundle\Config\ConfigLoader;
 use Terminal42\NotificationCenterBundle\Cron\PruneBulkyItemStorageCron;
 use Terminal42\NotificationCenterBundle\DependencyInjection\Terminal42NotificationCenterExtension;
@@ -59,6 +60,12 @@
         ])
     ;
 
+    $services->set(FileItemFactory::class)
+        ->args([
+            service('mime_types')->nullOnInvalid(),
+        ])
+    ;
+
     $services->set(PruneBulkyItemStorageCron::class)
         ->args([
             service(BulkyItemStorage::class),
diff --git a/contao/dca/tl_form.php b/contao/dca/tl_form.php
index 21829b65..89a41e83 100644
--- a/contao/dca/tl_form.php
+++ b/contao/dca/tl_form.php
@@ -17,6 +17,7 @@
  */
 $GLOBALS['TL_DCA']['tl_form']['fields']['nc_notification'] = [
     'exclude' => true,
+    'filter' => true,
     'inputType' => 'select',
     'eval' => ['includeBlankOption' => true, 'chosen' => true, 'tl_class' => 'clr w50'],
     'sql' => ['type' => 'integer', 'default' => 0, 'unsigned' => true],
diff --git a/src/BulkyItem/FileItem.php b/src/BulkyItem/FileItem.php
index dac914da..850ed53d 100644
--- a/src/BulkyItem/FileItem.php
+++ b/src/BulkyItem/FileItem.php
@@ -5,11 +5,14 @@
 namespace Terminal42\NotificationCenterBundle\BulkyItem;
 
 use Symfony\Component\Filesystem\Filesystem;
+use Terminal42\NotificationCenterBundle\Exception\BulkyItem\InvalidFileItemException;
 
 class FileItem implements BulkyItemInterface
 {
     /**
      * @param resource $contents
+     *
+     * @throws InvalidFileItemException
      */
     private function __construct(
         private $contents,
@@ -17,6 +20,9 @@ private function __construct(
         private readonly string $mimeType,
         private readonly int $size,
     ) {
+        $this->assert('' !== $this->name, 'Name must not be empty');
+        $this->assert('' !== $this->mimeType, 'Mime type must not be empty');
+        $this->assert($this->size >= 0, 'File size must not be smaller than 0');
     }
 
     public function getName(): string
@@ -53,10 +59,13 @@ public static function restore($contents, array $meta): BulkyItemInterface
         return new self($contents, $meta['name'], $meta['type'], $meta['size']);
     }
 
+    /**
+     * @throws InvalidFileItemException
+     */
     public static function fromPath(string $path, string $name, string $mimeType, int $size): self
     {
         if (!(new Filesystem())->exists($path)) {
-            throw new \InvalidArgumentException(\sprintf('The file "%s" does not exist.', $path));
+            throw new InvalidFileItemException(\sprintf('The file "%s" does not exist.', $path));
         }
 
         return new self(fopen($path, 'r'), $name, $mimeType, $size);
@@ -64,13 +73,22 @@ public static function fromPath(string $path, string $name, string $mimeType, in
 
     /**
      * @param resource $resource
+     *
+     * @throws InvalidFileItemException
      */
     public static function fromStream($resource, string $name, string $mimeType, int $size): self
     {
         if (!\is_resource($resource)) {
-            throw new \InvalidArgumentException('$contents must be a resource.');
+            throw new InvalidFileItemException('$contents must be a resource.');
         }
 
         return new self($resource, $name, $mimeType, $size);
     }
+
+    private function assert(bool $condition, string $message): void
+    {
+        if (!$condition) {
+            throw new InvalidFileItemException($message);
+        }
+    }
 }
diff --git a/src/BulkyItem/FileItemFactory.php b/src/BulkyItem/FileItemFactory.php
new file mode 100644
index 00000000..b44484e2
--- /dev/null
+++ b/src/BulkyItem/FileItemFactory.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\BulkyItem;
+
+use Contao\CoreBundle\Filesystem\FilesystemItem;
+use Contao\CoreBundle\Filesystem\VirtualFilesystemInterface;
+use Symfony\Component\Filesystem\Filesystem;
+use Symfony\Component\Mime\MimeTypeGuesserInterface;
+use Terminal42\NotificationCenterBundle\Exception\BulkyItem\InvalidFileItemException;
+
+class FileItemFactory
+{
+    public function __construct(private readonly MimeTypeGuesserInterface|null $mimeTypeGuesser = null)
+    {
+    }
+
+    /**
+     * @throws InvalidFileItemException if the information cannot be fetched automatically (e.g. missing mime type guesser service)
+     */
+    public function createFromLocalPath(string $path): FileItem
+    {
+        if (!(new Filesystem())->exists($path)) {
+            throw new InvalidFileItemException(\sprintf('The file "%s" does not exist.', $path));
+        }
+
+        $name = basename($path);
+        $mimeType = (string) $this->mimeTypeGuesser?->guessMimeType($path);
+        $size = (int) filesize($path);
+
+        return FileItem::fromPath($path, $name, $mimeType, $size);
+    }
+
+    /**
+     * @throws InvalidFileItemException
+     */
+    public function createFromVfsFilesystemItem(FilesystemItem $file, VirtualFilesystemInterface $virtualFilesystem): FileItem
+    {
+        $stream = $virtualFilesystem->readStream($file->getPath());
+
+        return FileItem::fromStream($stream, $file->getName(), $file->getMimeType(), $file->getFileSize());
+    }
+}
diff --git a/src/Config/ConfigLoader.php b/src/Config/ConfigLoader.php
index 21771366..425f8eee 100644
--- a/src/Config/ConfigLoader.php
+++ b/src/Config/ConfigLoader.php
@@ -38,6 +38,11 @@ public function loadModule(int $id): ModuleConfig|null
         return $this->loadConfig($id, 'tl_module', ModuleConfig::class);
     }
 
+    public function loadForm(int $id): FormConfig|null
+    {
+        return $this->loadConfig($id, 'tl_form', FormConfig::class);
+    }
+
     /**
      * @return array<MessageConfig>
      */
diff --git a/src/Config/FormConfig.php b/src/Config/FormConfig.php
new file mode 100644
index 00000000..f8255f5d
--- /dev/null
+++ b/src/Config/FormConfig.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Config;
+
+class FormConfig extends AbstractConfig
+{
+}
diff --git a/src/DependencyInjection/CompilerPass/AbstractGatewayPass.php b/src/DependencyInjection/CompilerPass/AbstractGatewayPass.php
index df3441a9..069b2bee 100644
--- a/src/DependencyInjection/CompilerPass/AbstractGatewayPass.php
+++ b/src/DependencyInjection/CompilerPass/AbstractGatewayPass.php
@@ -9,6 +9,7 @@
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\DependencyInjection\Reference;
+use Terminal42\NotificationCenterBundle\BulkyItem\BulkyItemStorage;
 use Terminal42\NotificationCenterBundle\DependencyInjection\Terminal42NotificationCenterExtension;
 use Terminal42\NotificationCenterBundle\Gateway\AbstractGateway;
 use Terminal42\NotificationCenterBundle\NotificationCenter;
@@ -20,6 +21,7 @@ public function process(ContainerBuilder $container): void
         $taggedServices = $container->findTaggedServiceIds(Terminal42NotificationCenterExtension::GATEWAY_TAG);
         $locateableServices = [
             AbstractGateway::SERVICE_NAME_NOTIFICATION_CENTER => new Reference(NotificationCenter::class),
+            AbstractGateway::SERVICE_NAME_BULKY_ITEM_STORAGE => new Reference(BulkyItemStorage::class),
             AbstractGateway::SERVICE_NAME_SIMPLE_TOKEN_PARSER => new Reference('contao.string.simple_token_parser', ContainerInterface::NULL_ON_INVALID_REFERENCE),
             AbstractGateway::SERVICE_NAME_INSERT_TAG_PARSER => new Reference('contao.insert_tag.parser', ContainerInterface::NULL_ON_INVALID_REFERENCE),
         ];
diff --git a/src/EventListener/ProcessFormDataListener.php b/src/EventListener/ProcessFormDataListener.php
index 3c2e74cf..2465d675 100644
--- a/src/EventListener/ProcessFormDataListener.php
+++ b/src/EventListener/ProcessFormDataListener.php
@@ -9,8 +9,10 @@
 use Contao\Form;
 use Contao\StringUtil;
 use Terminal42\NotificationCenterBundle\BulkyItem\FileItem;
+use Terminal42\NotificationCenterBundle\Config\ConfigLoader;
 use Terminal42\NotificationCenterBundle\NotificationCenter;
 use Terminal42\NotificationCenterBundle\Parcel\Stamp\BulkyItemsStamp;
+use Terminal42\NotificationCenterBundle\Parcel\Stamp\FormConfigStamp;
 
 #[AsHook('processFormData')]
 class ProcessFormDataListener
@@ -18,6 +20,7 @@ class ProcessFormDataListener
     public function __construct(
         private readonly NotificationCenter $notificationCenter,
         private readonly FileUploadNormalizer $fileUploadNormalizer,
+        private readonly ConfigLoader $configLoader,
     ) {
     }
 
@@ -76,7 +79,7 @@ public function __invoke(array $submittedData, array $formData, array|null $file
                     FileItem::fromStream($file['stream'], $file['name'], $file['type'], $file['size']) :
                     FileItem::fromPath($file['tmp_name'], $file['name'], $file['type'], $file['size']);
 
-                $vouchers[] = $this->notificationCenter->getBulkyGoodsStorage()->store($fileItem);
+                $vouchers[] = $this->notificationCenter->getBulkyItemStorage()->store($fileItem);
             }
 
             $tokens['form_'.$k] = implode(',', $vouchers);
@@ -95,6 +98,12 @@ public function __invoke(array $submittedData, array $formData, array|null $file
             $stamps = $stamps->with(new BulkyItemsStamp($bulkyItemVouchers));
         }
 
+        $formConfig = $this->configLoader->loadForm((int) $form->id);
+
+        if (null !== $formConfig) {
+            $stamps = $stamps->with(new FormConfigStamp($formConfig));
+        }
+
         $this->notificationCenter->sendNotificationWithStamps((int) $formData['nc_notification'], $stamps);
     }
 }
diff --git a/src/Exception/BulkyItem/InvalidFileItemException.php b/src/Exception/BulkyItem/InvalidFileItemException.php
new file mode 100644
index 00000000..fe84df81
--- /dev/null
+++ b/src/Exception/BulkyItem/InvalidFileItemException.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Exception\BulkyItem;
+
+class InvalidFileItemException extends \InvalidArgumentException
+{
+}
diff --git a/src/Gateway/AbstractGateway.php b/src/Gateway/AbstractGateway.php
index 773e7e49..0f979f06 100644
--- a/src/Gateway/AbstractGateway.php
+++ b/src/Gateway/AbstractGateway.php
@@ -7,6 +7,7 @@
 use Contao\CoreBundle\InsertTag\InsertTagParser;
 use Contao\CoreBundle\String\SimpleTokenParser;
 use Psr\Container\ContainerInterface;
+use Terminal42\NotificationCenterBundle\BulkyItem\BulkyItemStorage;
 use Terminal42\NotificationCenterBundle\Exception\Parcel\CouldNotDeliverParcelException;
 use Terminal42\NotificationCenterBundle\Exception\Parcel\CouldNotSealParcelException;
 use Terminal42\NotificationCenterBundle\NotificationCenter;
@@ -20,6 +21,8 @@ abstract class AbstractGateway implements GatewayInterface
 {
     public const SERVICE_NAME_NOTIFICATION_CENTER = 'notification_center';
 
+    public const SERVICE_NAME_BULKY_ITEM_STORAGE = 'bulky_item_storage';
+
     public const SERVICE_NAME_SIMPLE_TOKEN_PARSER = 'simple_token_parser';
 
     public const SERVICE_NAME_INSERT_TAG_PARSER = 'insert_tag_parser';
@@ -83,15 +86,23 @@ protected function replaceTokens(Parcel $parcel, string $value): string
             return $value;
         }
 
-        return $this->getSimpleTokenParser()?->parse(
-            $value,
-            $parcel->getStamp(TokenCollectionStamp::class)->tokenCollection->forSimpleTokenParser(),
-        );
+        if ($simpleTokenParser = $this->getSimpleTokenParser()) {
+            return $simpleTokenParser->parse(
+                $value,
+                $parcel->getStamp(TokenCollectionStamp::class)->tokenCollection->forSimpleTokenParser(),
+            );
+        }
+
+        return $value;
     }
 
     protected function replaceInsertTags(string $value): string
     {
-        return $this->getInsertTagParser()?->replaceInline($value);
+        if ($insertTagParser = $this->getInsertTagParser()) {
+            return $insertTagParser->replaceInline($value);
+        }
+
+        return $value;
     }
 
     protected function replaceTokensAndInsertTags(Parcel $parcel, string $value): string
@@ -143,4 +154,15 @@ protected function getNotificationCenter(): NotificationCenter|null
 
         return !$notificationCenter instanceof NotificationCenter ? null : $notificationCenter;
     }
+
+    protected function getBulkyItemStorage(): BulkyItemStorage|null
+    {
+        if (null === $this->container || !$this->container->has(self::SERVICE_NAME_BULKY_ITEM_STORAGE)) {
+            return null;
+        }
+
+        $bulkyItemStorage = $this->container->get(self::SERVICE_NAME_BULKY_ITEM_STORAGE);
+
+        return !$bulkyItemStorage instanceof BulkyItemStorage ? null : $bulkyItemStorage;
+    }
 }
diff --git a/src/Gateway/MailerGateway.php b/src/Gateway/MailerGateway.php
index 2b6c4231..0d971a3c 100644
--- a/src/Gateway/MailerGateway.php
+++ b/src/Gateway/MailerGateway.php
@@ -6,7 +6,7 @@
 
 use Contao\Controller;
 use Contao\CoreBundle\Filesystem\Dbafs\UnableToResolveUuidException;
-use Contao\CoreBundle\Filesystem\VirtualFilesystem;
+use Contao\CoreBundle\Filesystem\VirtualFilesystemInterface;
 use Contao\CoreBundle\Framework\ContaoFramework;
 use Contao\CoreBundle\Util\LocaleUtil;
 use Contao\FrontendTemplate;
@@ -33,7 +33,7 @@ class MailerGateway extends AbstractGateway
 
     public function __construct(
         private readonly ContaoFramework $contaoFramework,
-        private readonly VirtualFilesystem $filesystem,
+        private readonly VirtualFilesystemInterface $filesStorage,
         private readonly MailerInterface $mailer,
     ) {
     }
@@ -143,6 +143,7 @@ private function createEmailStamp(Parcel $parcel): EmailStamp
         $stamp = $stamp->withText($text);
 
         if ($html) {
+            $html = $this->embedImages($html, $stamp);
             $stamp = $stamp->withHtml($html);
         }
 
@@ -176,7 +177,7 @@ private function createEmail(Parcel $parcel): Email
 
         // Attachments
         foreach ($emailStamp->getAttachmentVouchers() as $voucher) {
-            $item = $this->getNotificationCenter()->getBulkyGoodsStorage()->retrieve($voucher);
+            $item = $this->getBulkyItemStorage()?->retrieve($voucher);
 
             if ($item instanceof FileItem) {
                 $email->attach(
@@ -187,6 +188,14 @@ private function createEmail(Parcel $parcel): Email
             }
         }
 
+        // Embedded images
+        foreach ($emailStamp->getEmbeddedImageVouchers() as $voucher) {
+            $item = $this->getBulkyItemStorage()?->retrieve($voucher);
+            if ($item instanceof FileItem) {
+                $email->attach($item->getContents(), $this->encodeVoucherForContentId($voucher));
+            }
+        }
+
         return $email;
     }
 
@@ -267,30 +276,17 @@ private function copyBackendAttachments(Parcel $parcel, LanguageConfig $language
 
             try {
                 $uuidObject = Uuid::isValid($uuid) ? Uuid::fromString($uuid) : Uuid::fromBinary($uuid);
-
-                if (null === ($item = $this->filesystem->get($uuidObject))) {
-                    continue;
-                }
             } catch (\InvalidArgumentException|UnableToResolveUuidException) {
                 continue;
             }
 
-            if (!$item->isFile()) {
+            $voucher = $this->createBulkyItemStorageVoucher($uuidObject, $this->filesStorage);
+
+            if (null === $voucher) {
                 continue;
             }
 
-            $voucher = $this->getNotificationCenter()?->getBulkyGoodsStorage()->store(
-                FileItem::fromStream(
-                    $this->filesystem->readStream($uuidObject),
-                    $item->getName(),
-                    $item->getMimeType(),
-                    $item->getFileSize(),
-                ),
-            );
-
-            if (null !== $voucher) {
-                $vouchers[] = $voucher;
-            }
+            $vouchers[] = $voucher;
         }
 
         if (0 === \count($vouchers)) {
@@ -299,4 +295,59 @@ private function copyBackendAttachments(Parcel $parcel, LanguageConfig $language
 
         return $parcel->withStamp(new BackendAttachmentsStamp($vouchers));
     }
+
+    private function createBulkyItemStorageVoucher(Uuid|string $location, VirtualFilesystemInterface $filesystem): string|null
+    {
+        try {
+            if (null === ($item = $filesystem->get($location))) {
+                return null;
+            }
+        } catch (\InvalidArgumentException|UnableToResolveUuidException) {
+            return null;
+        }
+
+        if (!$item->isFile()) {
+            return null;
+        }
+
+        return $this->getBulkyItemStorage()?->store(
+            FileItem::fromStream(
+                $filesystem->readStream($location),
+                $item->getName(),
+                $item->getMimeType(),
+                $item->getFileSize(),
+            ),
+        );
+    }
+
+    private function encodeVoucherForContentId(string $voucher): string
+    {
+        return rawurlencode($voucher);
+    }
+
+    private function embedImages(string $html, EmailStamp &$stamp): string
+    {
+        $prefixToStrip = '';
+
+        if (method_exists($this->filesStorage, 'getPrefix')) {
+            $prefixToStrip = $this->filesStorage->getPrefix();
+        }
+
+        return preg_replace_callback(
+            '/<[a-z][a-z0-9]*\b[^>]*((src=|background=|url\()["\']??)(.+\.(jpe?g|png|gif|bmp|tiff?|swf))(["\' ]??(\)??))[^>]*>/Ui',
+            function ($matches) use (&$stamp, $prefixToStrip) {
+                $location = ltrim(ltrim(ltrim($matches[3], '/'), $prefixToStrip), '/');
+                $voucher = $this->createBulkyItemStorageVoucher($location, $this->filesStorage);
+
+                if (null === $voucher) {
+                    return $matches[0];
+                }
+
+                $stamp = $stamp->withEmbeddedImageVoucher($voucher);
+
+                return str_replace($matches[3], 'cid:'.$this->encodeVoucherForContentId($voucher), $matches[0]);
+            },
+            $html,
+        );
+    }
 }
diff --git a/src/NotificationCenter.php b/src/NotificationCenter.php
index 5345ad38..a69bbe63 100644
--- a/src/NotificationCenter.php
+++ b/src/NotificationCenter.php
@@ -50,7 +50,7 @@ public function __construct(
         private readonly ConfigLoader $configLoader,
         private readonly EventDispatcherInterface $eventDispatcher,
         private readonly RequestStack $requestStack,
-        private readonly BulkyItemStorage $bulkyGoodsStorage,
+        private readonly BulkyItemStorage $bulkyItemStorage,
         private readonly StringParser $stringParser,
         private readonly LocaleSwitcher|null $localeSwitcher,
     ) {
@@ -58,7 +58,14 @@ public function __construct(
 
     public function getBulkyGoodsStorage(): BulkyItemStorage
     {
-        return $this->bulkyGoodsStorage;
+        trigger_deprecation('terminal42/notification_center', '2.1', 'Using "getBulkyGoodsStorage()" is deprecated, use "getBulkyItemStorage()" instead.');
+
+        return $this->bulkyItemStorage;
+    }
+
+    public function getBulkyItemStorage(): BulkyItemStorage
+    {
+        return $this->bulkyItemStorage;
     }
 
     /**
diff --git a/src/Parcel/Stamp/FormConfigStamp.php b/src/Parcel/Stamp/FormConfigStamp.php
new file mode 100644
index 00000000..c0fc06dc
--- /dev/null
+++ b/src/Parcel/Stamp/FormConfigStamp.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Parcel\Stamp;
+
+use Terminal42\NotificationCenterBundle\Config\FormConfig;
+
+class FormConfigStamp extends AbstractConfigStamp
+{
+    public function __construct(public FormConfig $formConfig)
+    {
+        parent::__construct($this->formConfig);
+    }
+
+    public static function fromArray(array $data): self
+    {
+        return new self(FormConfig::fromArray($data));
+    }
+}
diff --git a/src/Parcel/Stamp/Mailer/EmailStamp.php b/src/Parcel/Stamp/Mailer/EmailStamp.php
index 4c46c214..e7a61bec 100644
--- a/src/Parcel/Stamp/Mailer/EmailStamp.php
+++ b/src/Parcel/Stamp/Mailer/EmailStamp.php
@@ -34,6 +34,11 @@ class EmailStamp implements StampInterface
      */
     private array $attachmentVouchers = [];
 
+    /**
+     * @var array<string>
+     */
+    private array $embeddedImageVouchers = [];
+
     public function withFromName(string $fromName): self
     {
         $clone = clone $this;
@@ -106,6 +111,22 @@ public function withHtml(string $html): self
         return $clone;
     }
 
+    /**
+     * @return array<string>
+     */
+    public function getEmbeddedImageVouchers(): array
+    {
+        return $this->embeddedImageVouchers;
+    }
+
+    public function withEmbeddedImageVoucher(string $voucher): self
+    {
+        $clone = clone $this;
+        $clone->embeddedImageVouchers[] = $voucher;
+
+        return $clone;
+    }
+
     public function withAttachmentVoucher(string $voucher): self
     {
         $clone = clone $this;
@@ -170,6 +191,7 @@ public function toArray(): array
             'text' => $this->text,
             'html' => $this->html,
             'attachmentVouchers' => $this->attachmentVouchers,
+            'embeddedImageVouchers' => $this->embeddedImageVouchers,
         ];
     }
 
@@ -187,10 +209,14 @@ public static function fromArray(array $data): StampInterface
             ->withHtml($data['html'])
         ;
 
-        foreach ($data['attachmentVouchers'] as $voucher) {
+        foreach ($data['attachmentVouchers'] ?? [] as $voucher) {
             $stamp = $stamp->withAttachmentVoucher($voucher);
         }
 
+        foreach ($data['embeddedImageVouchers'] ?? [] as $voucher) {
+            $stamp = $stamp->withEmbeddedImageVoucher($voucher);
+        }
+
         return $stamp;
     }
 }
diff --git a/src/Token/TokenCollection.php b/src/Token/TokenCollection.php
index 0bc5fd68..b432436f 100644
--- a/src/Token/TokenCollection.php
+++ b/src/Token/TokenCollection.php
@@ -29,6 +29,19 @@ public static function fromSerializedArray(array $data): self
         return new self($tokens);
     }
 
+    public function replaceToken(Token $token): self
+    {
+        $existing = $this->getByName($token->getName());
+
+        if (null !== $existing) {
+            $this->remove($existing);
+        }
+
+        $this->addToken($token);
+
+        return $this;
+    }
+
     /**
      * Provides a fluent interface alternative to add() with a type hint.
      */
diff --git a/tests/BulkyItem/FileItemFactoryTest.php b/tests/BulkyItem/FileItemFactoryTest.php
new file mode 100644
index 00000000..08eeb8ae
--- /dev/null
+++ b/tests/BulkyItem/FileItemFactoryTest.php
@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test\BulkyItem;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mime\MimeTypes;
+use Terminal42\NotificationCenterBundle\BulkyItem\FileItemFactory;
+use Terminal42\NotificationCenterBundle\Test\VirtualFilesystemTestTrait;
+
+class FileItemFactoryTest extends TestCase
+{
+    use VirtualFilesystemTestTrait;
+
+    public function testCreateFromLocalPath(): void
+    {
+        $factory = new FileItemFactory(new MimeTypes());
+        $item = $factory->createFromLocalPath(__DIR__.'/../Fixtures/name.jpg');
+        $this->assertSame('name.jpg', $item->getName());
+        $this->assertSame('image/jpeg', $item->getMimeType());
+        $this->assertSame(333, $item->getSize());
+        $this->assertIsResource($item->getContents());
+    }
+
+    public function testCreateFromVfsFilesystemItem(): void
+    {
+        $vfsCollection = $this->createVfsCollection();
+        $vfs = $vfsCollection->get('files');
+        $vfs->write('media/name.jpg', file_get_contents(__DIR__.'/../Fixtures/name.jpg'));
+
+        $item = $vfs->get('media/name.jpg');
+
+        $factory = new FileItemFactory(new MimeTypes());
+        $item = $factory->createFromVfsFilesystemItem($item, $vfs);
+        $this->assertSame('name.jpg', $item->getName());
+        $this->assertSame('image/jpeg', $item->getMimeType());
+        $this->assertSame(333, $item->getSize());
+        $this->assertIsResource($item->getContents());
+    }
+}
diff --git a/tests/BulkyItem/FileItemTest.php b/tests/BulkyItem/FileItemTest.php
new file mode 100644
index 00000000..c63c2dd4
--- /dev/null
+++ b/tests/BulkyItem/FileItemTest.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test\BulkyItem;
+
+use PHPUnit\Framework\TestCase;
+use Terminal42\NotificationCenterBundle\BulkyItem\FileItem;
+use Terminal42\NotificationCenterBundle\Exception\BulkyItem\InvalidFileItemException;
+
+class FileItemTest extends TestCase
+{
+    public function testCannotCreateEmptyNameFileItem(): void
+    {
+        $this->expectException(InvalidFileItemException::class);
+        $this->expectExceptionMessage('Name must not be empty');
+
+        FileItem::fromPath(__DIR__.'/../Fixtures/name.jpg', '', 'image/jpg', 0);
+    }
+
+    public function testCannotCreateEmptyMimeTypeFileItem(): void
+    {
+        $this->expectException(InvalidFileItemException::class);
+        $this->expectExceptionMessage('Mime type must not be empty');
+
+        FileItem::fromPath(__DIR__.'/../Fixtures/name.jpg', 'name.jpg', '', 0);
+    }
+
+    public function testCannotCreateInvalidFileSizeFileItem(): void
+    {
+        $this->expectException(InvalidFileItemException::class);
+        $this->expectExceptionMessage('File size must not be smaller than 0');
+
+        FileItem::fromPath(__DIR__.'/../Fixtures/name.jpg', 'name.jpg', 'image/jpg', -42);
+    }
+}
diff --git a/tests/BulkyItem/InMemoryDbafs.php b/tests/BulkyItem/InMemoryDbafs.php
new file mode 100644
index 00000000..3c3568a4
--- /dev/null
+++ b/tests/BulkyItem/InMemoryDbafs.php
@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test\BulkyItem;
+
+use Contao\CoreBundle\Filesystem\Dbafs\ChangeSet\ChangeSet;
+use Contao\CoreBundle\Filesystem\Dbafs\DbafsInterface;
+use Contao\CoreBundle\Filesystem\FilesystemItem;
+use Symfony\Component\Uid\Uuid;
+
+class InMemoryDbafs implements DbafsInterface
+{
+    /**
+     * @var array<string, FilesystemItem>
+     */
+    private array $records = [];
+
+    /**
+     * @var array<string, array<mixed>>
+     */
+    private array $meta = [];
+
+    public function getPathFromUuid(Uuid $uuid): string|null
+    {
+        throw new \RuntimeException('Not implemented');
+    }
+
+    public function getRecord(string $path): FilesystemItem|null
+    {
+        if (isset($this->records[$path])) {
+            return new FilesystemItem(
+                true,
+                $path,
+                null,
+                null,
+                null,
+                $this->meta[$path] ?? [],
+            );
+        }
+
+        return null;
+    }
+
+    public function getRecords(string $path, bool $deep = false): iterable
+    {
+        throw new \RuntimeException('Not implemented');
+    }
+
+    public function setExtraMetadata(string $path, array $metadata): void
+    {
+        $this->meta[$path] = $metadata;
+    }
+
+    public function sync(string ...$paths): ChangeSet
+    {
+        foreach ($paths as $path) {
+            $this->records[$path] = true;
+        }
+
+        return new ChangeSet([], [], []);
+    }
+
+    public function getSupportedFeatures(): int
+    {
+        return DbafsInterface::FEATURES_NONE;
+    }
+}
diff --git a/tests/BulkyItem/VirtualFilesystemCollection.php b/tests/BulkyItem/VirtualFilesystemCollection.php
new file mode 100644
index 00000000..594e95b6
--- /dev/null
+++ b/tests/BulkyItem/VirtualFilesystemCollection.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test\BulkyItem;
+
+use Contao\CoreBundle\Filesystem\VirtualFilesystem;
+
+class VirtualFilesystemCollection
+{
+    /**
+     * @param array<string, VirtualFilesystem> $vfs
+     */
+    public function __construct(private array $vfs = [])
+    {
+    }
+
+    public function get(string $name): VirtualFilesystem
+    {
+        return $this->vfs[$name];
+    }
+
+    public function add(VirtualFilesystem $vfs): self
+    {
+        $this->vfs[$vfs->getPrefix()] = $vfs;
+
+        return $this;
+    }
+}
diff --git a/tests/EventListener/AdminEmailTokenListenerTest.php b/tests/EventListener/AdminEmailTokenListenerTest.php
index 40d69242..aaf30e9a 100644
--- a/tests/EventListener/AdminEmailTokenListenerTest.php
+++ b/tests/EventListener/AdminEmailTokenListenerTest.php
@@ -8,7 +8,6 @@
 use Contao\CoreBundle\Framework\ContaoFramework;
 use Contao\PageModel;
 use Contao\TestCase\ContaoTestCase;
-use PHPUnit\Framework\Attributes\DataProvider;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\RequestStack;
 use Terminal42\NotificationCenterBundle\Config\MessageConfig;
@@ -21,7 +20,9 @@
 
 class AdminEmailTokenListenerTest extends ContaoTestCase
 {
-    #[DataProvider('adminEmailProvider')]
+    /**
+     * @dataProvider adminEmailProvider
+     */
     public function testAddsAdminTokens(string $configFriendlyEmail, string $pageFriendlyEmail, string $expectedName, string $expectedEmail): void
     {
         $pageModel = $this->mockClassWithProperties(PageModel::class, [
@@ -46,7 +47,10 @@ public function testAddsAdminTokens(string $configFriendlyEmail, string $pageFri
         $this->assertSame($expectedEmail, $tokenCollection->getByName('admin_email')->getValue());
     }
 
-    public static function adminEmailProvider(): \Generator
+    /**
+     * @return iterable<array{0: string, 1: string, 2: string, 3: string}>
+     */
+    public static function adminEmailProvider(): iterable
     {
         yield 'Basic admin email in config' => [
             'foobar-config@terminal42.ch',
diff --git a/tests/Gateway/MailerGatewayTest.php b/tests/Gateway/MailerGatewayTest.php
new file mode 100644
index 00000000..94d96de2
--- /dev/null
+++ b/tests/Gateway/MailerGatewayTest.php
@@ -0,0 +1,168 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test\Gateway;
+
+use Contao\Controller;
+use Contao\CoreBundle\Filesystem\Dbafs\DbafsManager;
+use Contao\CoreBundle\Filesystem\MountManager;
+use Contao\CoreBundle\Filesystem\VirtualFilesystem;
+use Contao\CoreBundle\Framework\ContaoFramework;
+use Contao\CoreBundle\String\SimpleTokenParser;
+use Contao\FrontendTemplate;
+use Contao\TestCase\ContaoTestCase;
+use League\Flysystem\InMemory\InMemoryFilesystemAdapter;
+use Symfony\Component\DependencyInjection\Container;
+use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
+use Symfony\Component\Mailer\MailerInterface;
+use Symfony\Component\Mime\Email;
+use Terminal42\NotificationCenterBundle\BulkyItem\BulkyItemStorage;
+use Terminal42\NotificationCenterBundle\Config\LanguageConfig;
+use Terminal42\NotificationCenterBundle\Config\MessageConfig;
+use Terminal42\NotificationCenterBundle\Gateway\AbstractGateway;
+use Terminal42\NotificationCenterBundle\Gateway\MailerGateway;
+use Terminal42\NotificationCenterBundle\Parcel\Parcel;
+use Terminal42\NotificationCenterBundle\Parcel\Stamp\LanguageConfigStamp;
+use Terminal42\NotificationCenterBundle\Parcel\Stamp\TokenCollectionStamp;
+use Terminal42\NotificationCenterBundle\Test\BulkyItem\InMemoryDbafs;
+use Terminal42\NotificationCenterBundle\Test\BulkyItem\VirtualFilesystemCollection;
+use Terminal42\NotificationCenterBundle\Token\Token;
+use Terminal42\NotificationCenterBundle\Token\TokenCollection;
+
+class MailerGatewayTest extends ContaoTestCase
+{
+    /**
+     * @dataProvider embeddingHtmlImagesProvider
+     *
+     * @param array<string, string> $mockFiles
+     * @param array<string, string> $expectedAttachmentsContentsAndPath
+     */
+    public function testEmbeddingHtmlImages(string $parsedTemplateHtml, array $mockFiles, array $expectedAttachmentsContentsAndPath): void
+    {
+        $vfsCollection = $this->createVfsCollection();
+
+        foreach ($mockFiles as $path => $contents) {
+            $vfsCollection->get('files')->write($path, $contents);
+        }
+
+        $mailer = $this->createMock(MailerInterface::class);
+        $mailer
+            ->expects($this->once())
+            ->method('send')
+            ->with($this->callback(
+                static function (Email $email) use ($parsedTemplateHtml, $expectedAttachmentsContentsAndPath): bool {
+                    $attachments = [];
+
+                    foreach ($email->getAttachments() as $attachment) {
+                        $attachments[$attachment->getBody()] = $attachment->getName();
+                    }
+
+                    $expectedHtml = $parsedTemplateHtml;
+
+                    foreach ($expectedAttachmentsContentsAndPath as $content => $path) {
+                        $expectedHtml = str_replace($path, 'cid:'.$attachments[$content], $expectedHtml);
+                    }
+
+                    return $expectedHtml === $email->getHtmlBody();
+                },
+            ))
+        ;
+
+        $tokenCollection = new TokenCollection();
+        $tokenCollection->addToken(Token::fromValue('admin_email', 'foobar@example.com'));
+        $tokenCollection->addToken(Token::fromValue('recipient_email', 'foobar@example.com'));
+
+        $parcel = new Parcel(MessageConfig::fromArray([
+            'email_template' => 'mail_default',
+        ]));
+        $parcel = $parcel->withStamp(new LanguageConfigStamp(LanguageConfig::fromArray([
+            'recipients' => '##recipient_email##',
+            'email_mode' => 'textAndHtml',
+        ])));
+        $parcel = $parcel->withStamp(new TokenCollectionStamp($tokenCollection));
+
+        $gateway = new MailerGateway(
+            $this->createFrameWorkWithTemplate($parsedTemplateHtml),
+            $vfsCollection->get('files'),
+            $mailer,
+        );
+        $container = new Container();
+        $container->set(AbstractGateway::SERVICE_NAME_BULKY_ITEM_STORAGE, new BulkyItemStorage($vfsCollection->get('bulky_item')));
+        $container->set(AbstractGateway::SERVICE_NAME_SIMPLE_TOKEN_PARSER, new SimpleTokenParser(new ExpressionLanguage()));
+        $gateway->setContainer($container);
+
+        $parcel = $gateway->sealParcel($parcel);
+        $gateway->sendParcel($parcel);
+    }
+
+    /**
+     * @return iterable<array{0: string, 1: array<string, string>, 2: array<string, string>}>
+     */
+    public static function embeddingHtmlImagesProvider(): iterable
+    {
+        yield 'Test embeds a relative upload path' => [
+            '<html><body><p><img src="files/contaodemo/media/content-images/DSC_5276.jpg" alt="" width="800" height="533"></p></body></html>',
+            [
+                'contaodemo/media/content-images/DSC_5276.jpg' => 'foobar',
+            ],
+            [
+                'foobar' => 'files/contaodemo/media/content-images/DSC_5276.jpg',
+            ],
+        ];
+
+        yield 'Test embeds an absolute upload path' => [
+            '<html><body><p><img src="/files/contaodemo/media/content-images/DSC_5276.jpg" alt="" width="800" height="533"></p></body></html>',
+            [
+                'contaodemo/media/content-images/DSC_5276.jpg' => 'foobar',
+            ],
+            [
+                'foobar' => '/files/contaodemo/media/content-images/DSC_5276.jpg',
+            ],
+        ];
+    }
+
+    private function createVfsCollection(): VirtualFilesystemCollection
+    {
+        $mountManager = (new MountManager())
+            ->mount(new InMemoryFilesystemAdapter(), 'files')
+            ->mount(new InMemoryFilesystemAdapter(), 'bulky_item')
+        ;
+
+        $dbafsManager = new DbafsManager();
+        $dbafsManager->register(new InMemoryDbafs(), 'files');
+        $dbafsManager->register(new InMemoryDbafs(), 'bulky_item');
+
+        $vfsCollection = new VirtualFilesystemCollection();
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, 'files'));
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, 'bulky_item'));
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, '')); // Global one
+
+        return $vfsCollection;
+    }
+
+    private function createFrameWorkWithTemplate(string $parsedTemplateHtml): ContaoFramework
+    {
+        $controllerAdapter = $this->mockAdapter(['convertRelativeUrls']);
+        $controllerAdapter
+            ->method('convertRelativeUrls')
+            ->willReturnCallback(static fn (string $template): string => $template)
+        ;
+
+        $templateInstance = $this->createMock(FrontendTemplate::class);
+        $templateInstance
+            ->expects($this->once())
+            ->method('parse')
+            ->willReturn($parsedTemplateHtml)
+        ;
+
+        return $this->mockContaoFramework(
+            [
+                Controller::class => $controllerAdapter,
+            ],
+            [
+                FrontendTemplate::class => $templateInstance,
+            ],
+        );
+    }
+}
diff --git a/tests/Token/TokenCollectionTest.php b/tests/Token/TokenCollectionTest.php
index 9e16176b..6dd27aaf 100644
--- a/tests/Token/TokenCollectionTest.php
+++ b/tests/Token/TokenCollectionTest.php
@@ -61,6 +61,23 @@ public function testCollectionHandling(): void
         $this->assertNull($tokenCollection->getByName('form_i_do_not_exist'));
     }
 
+    public function testReplace(): void
+    {
+        $tokenCollection = new TokenCollection();
+        $tokenCollection->addToken(Token::fromValue('test', 'foobar'));
+        $tokenCollection->addToken(Token::fromValue('test', 'foobar new'));
+
+        $this->assertCount(2, $tokenCollection);
+        $this->assertSame('foobar', $tokenCollection->getByName('test')->getValue(), 'foobar');
+
+        $tokenCollection = new TokenCollection();
+        $tokenCollection->replaceToken(Token::fromValue('test', 'foobar'));
+        $tokenCollection->replaceToken(Token::fromValue('test', 'foobar new'));
+
+        $this->assertCount(1, $tokenCollection);
+        $this->assertSame('foobar new', $tokenCollection->getByName('test')->getValue(), 'foobar');
+    }
+
     public function testMerge(): void
     {
         $tokenCollectionA = new TokenCollection();
diff --git a/tests/Token/TokenTest.php b/tests/Token/TokenTest.php
index de5ab067..58e68c50 100644
--- a/tests/Token/TokenTest.php
+++ b/tests/Token/TokenTest.php
@@ -10,7 +10,9 @@
 
 class TokenTest extends TestCase
 {
-    #[DataProvider('anythingProvider')]
+    /**
+     * @dataProvider anythingProvider
+     */
     public function testFromAnything(mixed $value, string $expectedParserValue): void
     {
         $token = Token::fromValue('token', $value);
@@ -19,16 +21,20 @@ public function testFromAnything(mixed $value, string $expectedParserValue): voi
     }
 
     /**
+     * @dataProvider arrayProvider
+     *
      * @param array<mixed> $value
      */
-    #[DataProvider('arrayProvider')]
     public function testArrayParserFormat(array $value, string $expectedParserValue): void
     {
         $token = Token::fromValue('form_foobar', $value);
         $this->assertSame($expectedParserValue, $token->getParserValue());
     }
 
-    public static function arrayProvider(): \Generator
+    /**
+     * @return iterable<array{0: array<mixed>, 1: string}>
+     */
+    public static function arrayProvider(): iterable
     {
         yield 'Simple list array token' => [
             [
@@ -62,7 +68,10 @@ public static function arrayProvider(): \Generator
         ];
     }
 
-    public static function anythingProvider(): \Generator
+    /**
+     * @return iterable<array{0: mixed, 1: string}>
+     */
+    public static function anythingProvider(): iterable
     {
         yield [
             'foobar',
diff --git a/tests/VirtualFilesystemTestTrait.php b/tests/VirtualFilesystemTestTrait.php
new file mode 100644
index 00000000..aeb7d07f
--- /dev/null
+++ b/tests/VirtualFilesystemTestTrait.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Terminal42\NotificationCenterBundle\Test;
+
+use Contao\CoreBundle\Filesystem\Dbafs\DbafsManager;
+use Contao\CoreBundle\Filesystem\MountManager;
+use Contao\CoreBundle\Filesystem\VirtualFilesystem;
+use League\Flysystem\InMemory\InMemoryFilesystemAdapter;
+use Terminal42\NotificationCenterBundle\Test\BulkyItem\InMemoryDbafs;
+use Terminal42\NotificationCenterBundle\Test\BulkyItem\VirtualFilesystemCollection;
+
+trait VirtualFilesystemTestTrait
+{
+    private function createVfsCollection(): VirtualFilesystemCollection
+    {
+        $mountManager = (new MountManager())
+            ->mount(new InMemoryFilesystemAdapter(), 'files')
+            ->mount(new InMemoryFilesystemAdapter(), 'bulky_item')
+        ;
+
+        $dbafsManager = new DbafsManager();
+        $dbafsManager->register(new InMemoryDbafs(), 'files');
+        $dbafsManager->register(new InMemoryDbafs(), 'bulky_item');
+
+        $vfsCollection = new VirtualFilesystemCollection();
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, 'files'));
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, 'bulky_item'));
+        $vfsCollection->add(new VirtualFilesystem($mountManager, $dbafsManager, '')); // Global one
+
+        return $vfsCollection;
+    }
+}