diff --git a/demo/site/package.json b/demo/site/package.json
index ab4e81c1982..253b2b464ca 100644
--- a/demo/site/package.json
+++ b/demo/site/package.json
@@ -47,6 +47,7 @@
         "filesize": "^10.1.6",
         "ioredis": "^5.10.1",
         "lru-cache": "^11.5.1",
+        "mjml": "^4.18.0",
         "next": "^16.2.10",
         "react": "^19.2.6",
         "react-dom": "^19.2.6",
diff --git a/knip.json b/knip.json
index 7f076af2402..fe6e1318daf 100644
--- a/knip.json
+++ b/knip.json
@@ -107,7 +107,7 @@
         "demo/site": {
             "entry": ["./src/app/**", "./cache-handler.ts", "./server.ts", "./opentelemetry-metrics.ts", "tracing.dev.ts", "tracing.production.ts"],
             "project": ["./src/**/*.{ts,tsx}"],
-            "ignoreDependencies": ["@babel/core", "@types/grecaptcha"],
+            "ignoreDependencies": ["@babel/core", "@types/grecaptcha", "mjml"],
             "ignore": ["**/*.generated.ts"]
         },
         "storybook": {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index d6ace35437c..80832f11aa7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -566,6 +566,9 @@ importers:
       lru-cache:
         specifier: ^11.5.1
         version: 11.5.1
+      mjml:
+        specifier: ^4.18.0
+        version: 4.18.0
       next:
         specifier: ^16.2.10
         version: 16.2.10(@babel/core@7.29.7)(@opentelemetry/api@1.9.1)(react-dom@19.2.6(react@19.2.6))(react@19.2.6)(sass@1.93.0)