Adding a fake SMTP mail server
At the end of the docker-compose.yaml, we add the last service:
mailhog:     image: mailhog/mailhog:latest     expose:       - 1025       - 8025
The ports used will be 1025 for Django to connect to the SMTP server and 8025 for the web interface via the webmail.localhost domain because Caddy will act as a reverse proxy.
Now that we have added all the containers, it’s time to test whether the containers run and work with each other.