Graylog docker-compose with own network for frondend and smtp/relay

docker-compose.yaml

version: '2'
services:
    mongo:
        image: "mongo:3"
        volumes:
           - /volumes/graylog/mongo:/data/db
        networks: 
           - graylog  
    elasticsearch:
        image: "elasticsearch:2"
        command: "elasticsearch -Des.cluster.name='graylog'"
        volumes:
            - /volumes/graylog/elasticsearch:/usr/share/elasticsearch/data
        networks: 
            - graylog
    graylog:
        image: graylog-plugins
        volumes:
            - /volumes/graylog/journal:/usr/share/graylog/data/journal
            #- /volumes/graylog/config:/usr/share/graylog/data/config
        environment:
            GRAYLOG_PASSWORD_SECRET: xxxxxxxxxxxxxxxxxxxxxxxxxxxx
            GRAYLOG_ROOT_PASSWORD_SHA2: xxxxxxxxxxxxxxxxxxxxxxxxxxxx
            GRAYLOG_WEB_ENDPOINT_URI: https://example.tld/api/
            GRAYLOG_TRANSPORT_EMAIL_ENABLED: "true"
            GRAYLOG_TRANSPORT_EMAIL_HOSTNAME: smtp
            GRAYLOG_TRANSPORT_EMAIL_PORT: 25
            GRAYLOG_TRANSPORT_EMAIL_USE_AUTH: "false"
            GRAYLOG_TRANSPORT_EMAIL_USE_TLS: "false"
            GRAYLOG_TRANSPORT_EMAIL_USE_SSL: "false"
        depends_on:
          - mongo
          - elasticsearch
        networks: 
          - graylog  
        ports:
            - "127.0.0.1:9000:9000"
            - "12201/tcp:12201/tcp"
            - "12201/udp:12201/udp"
            - "1514/udp:1514/udp"
            - "5044:5044"
networks:
      graylog:
        external: true