docker/swarm/stack/kqueen_mail.yml

parameters:
  _param:
    mail_server_hostname: mail
  docker:
    client:
      stack:
        kqueen:
          service:
            mail:
              image: modularitycontainers/postfix
              environment:
                MYHOSTNAME: ${_param:mail_server_hostname}
          network:
            default:
              external:
                name: kqueen_backend