fix: use SMTP relay instead of forward with MP_SMTP_RELAY_ALL

- Change from MP_SMTP_FORWARD_* to MP_SMTP_RELAY_*
- Add MP_SMTP_RELAY_ALL=true to relay all emails
- Preserves original recipients (relay vs forward)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

net/compose.yaml

@@ -234,13 +234,14 @@ services:
       MP_SMTP_AUTH_ACCEPT_ANY: 1
       MP_SMTP_AUTH_ALLOW_INSECURE: 1
       MP_MAX_MESSAGES: 5000
-      # SMTP forwarding to IONOS via environment variables
-      MP_SMTP_FORWARD_HOST: ${EMAIL_SMTP_HOST}
-      MP_SMTP_FORWARD_PORT: ${EMAIL_SMTP_PORT}
-      MP_SMTP_FORWARD_USERNAME: ${EMAIL_SMTP_USER}
-      MP_SMTP_FORWARD_PASSWORD: ${EMAIL_SMTP_PASSWORD}
-      MP_SMTP_FORWARD_AUTH: plain
-      MP_SMTP_FORWARD_TLS: "true"
+      # SMTP relay to IONOS - relay all emails preserving recipients
+      MP_SMTP_RELAY_ALL: "true"
+      MP_SMTP_RELAY_HOST: ${EMAIL_SMTP_HOST}
+      MP_SMTP_RELAY_PORT: ${EMAIL_SMTP_PORT}
+      MP_SMTP_RELAY_USERNAME: ${EMAIL_SMTP_USER}
+      MP_SMTP_RELAY_PASSWORD: ${EMAIL_SMTP_PASSWORD}
+      MP_SMTP_RELAY_AUTH: plain
+      MP_SMTP_RELAY_TLS: "true"
     volumes:
       - mailpit_data:/data
     networks: