How to get container X to send all mail via the postfix container

[WillGibson]

@juanluisbaptiste We're nearing the end of "Dockerising" a legacy application.

The application uses Mailgun in itself to send emails, but we need to get the emails from any cron output (fatal errors etc.) sent out.

I am hoping we can do this with your docker-postfix image. I've got it running and sending email via Mailgun from itself, but have no idea how to configure the main application PHP container to route any emails cron would send via the postfix container.

Is this something you can advise on?

Our redacted Docker Compose file is as follows...

version: '2'

networks:
  application-network:

volumes:
  mysql:
    driver: local

services:

  mysql:
    image: mysql:5.5.58
    environment: &mysql_env
      XXXXXXXXXX
    restart: always
    volumes:
      - mysql:/var/lib/mysql
    networks:
      application-network:
        aliases:
         - XXXXXXXXXX

  php-apache:
    build:
      context: ../
      dockerfile: dockerfile/php-apache
    image: XXXXXXXXXX-php-apache-5.6.32:v1.1.1
    restart: always
    environment:
      <<: *mysql_env
    volumes:
      XXXXXXXXXX
    ports:
      - 33040:80
    depends_on:
      - mysql
      - postfix
    networks:
      application-network:

  postfix:
    image: juanluisbaptiste/postfix:latest
    expose:
      - 25
    environment:
      SMTP_SERVER: smtp.mailgun.org
      SMTP_USERNAME: postmaster@XXXXXXXXXX
      SMTP_PASSWORD: XXXXXXXXXX
      SERVER_HOSTNAME: XXXXXXXXXX
    networks:
      application-network:

[juanluisbaptiste]

Hi,

I think you just need to configure mailgun to use an external smtp server and configure the host to postfix, set port to 25, no user/password.

[WillGibson]

Thanks for the reply.

I'm confused, mail servers are not my thing to be honest, I have no experience setting them up.

Are you saying to configure our application container to use the host's Postfix instead of using juanluisbaptiste/docker-postfix?

[WillGibson]

Actually, we changed our approach and our deployment now creates the cron tasks on the host, running the command in the docker containers via Docker Compose, so now we don't need to faff around with postfix :-)