diff --git a/docker-compose.yml b/docker-compose.yml
index f3c9ec0..e5ea861 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -52,10 +52,14 @@ services:
   # ── Email: Python SMTP debug server (dev only) ────────────
   # Accepts all mail and prints it to stdout (docker compose logs smtp)
   smtp:
-    image: python:3-alpine
+    build:
+      context: .
+      dockerfile_inline: |
+        FROM python:3-alpine
+        RUN pip install aiosmtpd --quiet
+        CMD ["python", "-m", "aiosmtpd", "-n", "-l", "0.0.0.0:1025"]
     restart: unless-stopped
     profiles: ["dev"]
-    command: sh -c "pip install aiosmtpd --quiet && python -m aiosmtpd -n -l 0.0.0.0:${SMTP_PORT:-1025}"
     networks:
       - internal