$ bin/config get metamta.mail-adapter
{
  "config": [
    {
      "key": "metamta.mail-adapter",
      "source": "local",
      "value": null,
      "status": "unset",
      "errorInfo": null
    },
    {
      "key": "metamta.mail-adapter",
      "source": "database",
      "value": null,
      "status": "unset",
      "errorInfo": null
    }
  ]
}