We need the SMTP server for our mailer service. We use the juanluisbaptiste/postfix image with the Postfix mail server. The server also has to be restarted if it fails and we set the restart policy to always. Look at the following code:

smtp:
  image: juanluisbaptiste/postfix
  restart: always
  environment:
    - SMTP_SERVER=smtp.example.com
    - [email protected]
    - SMTP_PASSWORD=password
    - SERVER_HOSTNAME=smtp.example.com
  ports:
    - "2525:25"

We also configure the server using the environment variables and set the server name, username, password, and a hostname. To test the mail server, we forward port 25 of the mail server to a local 2525 port.