This container can be pulled via:
  docker pull registry.opensuse.org/opensuse/factory/zsystems/totest/containers/opensuse/postfix:3.9.0
  docker pull registry.opensuse.org/opensuse/factory/zsystems/totest/containers/opensuse/postfix:3.9.0-13.53

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.