/etc/grafana/grafana.ini is Readonly, I cannot update grafana.ini , need to config SMTP for email

Grafana Configuration
2

might this help? I would use the following approach

    volumes:
      - ./grafana:/etc/grafana/

and have your grafana.ini in the grafana folder on left. you could try this as in the docker run so that it pushes your customized ini to the container.

docker run -v ./grafana/grafana.ini:/etc/grafana/grafana.ini