Document email service configuration

README.md

@@ -1,4 +1,4 @@
-# Drivers Hub: Docker Deployment
+# Drivers Hub: Backend Docker Deployment
 
 ```text
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@@ -168,6 +168,43 @@ checks that both accounts use the same Steam ID. The `trackers` section in
 `config/config.json` configures telemetry services. It does not configure the
 TruckersMP account connection.
 
+### Email
+
+Configure SMTP if users must register with email, confirm or change an email
+address, or reset a password. Set the connection and login values in
+`config/config.json`:
+
+```json
+"smtp_host": "smtp.example.com",
+"smtp_port": "587",
+"smtp_email": "hub@example.com",
+"smtp_password": "replace with the SMTP password"
+```
+
+Use the host, submission port, user name, and password from your email
+provider. The `smtp_email` value is the SMTP login name. Some providers use an
+account name instead of an email address.
+
+Set the public frontend confirmation URL. Keep the `{secret}` placeholder:
+
+```json
+"frontend_urls": {
+    "email_confirm": "https://hub.example.com/auth/email?secret={secret}"
+}
+```
+
+Do not replace the other entries in `frontend_urls`. Change each `from_email`
+value in the `register`, `update_email`, and `reset_password` email templates
+to a valid sender. For example:
+
+```json
+"from_email": "Drivers Hub <hub@example.com>"
+```
+
+The SMTP password is a secret. Do not commit `config/config.json`. Restart the
+backend after you change the SMTP settings. Test email registration and
+password reset before you make email registration available to users.
+
 ### Registration and required connections
 
 Use `register_methods` in `config/config.json` to select the available