Please create a new file `data/conf/postfix/extra.cf` for overrides or additional content to `main.cf`. Postfix will complain about duplicate values once after starting postfix-mailcow, this is intended. Syslog-ng was configured to hide those warnings while Postfix is running, to not spam the log files with unnecessary information every time a service is used. Restart `postfix-mailcow` to apply your changes: ``` docker-compose restart postfix-mailcow ```