diff --git a/.gitignore b/.gitignore
index e3de4fa..b95710b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 ###> system7 - jotunheimr ###
+compose.override.yaml
 +bak/
 .idea/
 node_modules/
diff --git a/README.md b/README.md
index 464983a..08c554b 100644
--- a/README.md
+++ b/README.md
@@ -136,6 +136,44 @@ echo '' | mc pipe local/mineseeker/cache/.keep
 
 ---
 
+## Development environment
+
+When running the Docker stack locally you typically want to catch outgoing emails instead of relaying them through a real SMTP server.
+The production `compose.yaml` uses Postfix for actual mail delivery and must not be edited for local overrides.
+Use a `compose.override.yaml` file instead — Docker Compose merges it automatically on top of the base file whenever both are present.
+
+### Email: replace Postfix with MailHog
+
+Create `compose.override.yaml` in the project root (it is git-ignored and never reaches production):
+
+```yaml
+services:
+  app:
+    environment:
+      MAILER_DSN: smtp://mail:1025?verify_peer=0
+  mail:
+    image: mailhog/mailhog:latest
+    ports:
+      - "8025:8025"
+```
+
+This replaces the `mail` service image with MailHog and points the application's mailer at its SMTP port (`1025`).
+No other files need to change.
+
+After adding the file, restart the stack:
+
+```bash
+make start-build
+```
+
+All emails sent by the application are now captured by MailHog.
+Open the web UI at **http://localhost:8025** to inspect them.
+
+> **Production note** — `compose.override.yaml` is listed in `.gitignore`.
+> Never commit it; the production server must only see `compose.yaml` with Postfix.
+
+---
+
 ## License
 
 LGPL-3.0 — see [LICENSE](LICENSE) for details.