elasticsearch count records with conditions and range

gistfile1.txt

GET /filebeat-*/_search
{
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "host.hostname": {
              "value": "mail"
            }
          }
        },
        {
          "match": {
            "message": "[inputs.postfix] Error in plugin"
          }
        },
        {
          "range": {
            "@timestamp": {
              "gte": "2020-12-17T09:00:00.000Z",
              "lte": "2020-12-17T10:00:00.000Z"
            }
          }
        }
      ]
    }
  }
}