POST users/user
{
    "name" :"SMITH",
    "emails" : [
       "[email protected]"
    ]
}

POST users/user
{
    "name" :"SMITH",
    "emails" : [
      "[email protected]",
      "[email protected]"
    ]
}

POST users/_search
{
  "size": 0,
  "aggs": {
    "duplicateCount": {
      "terms": {
        "script": {
          "inline": "doc['emails.keyword'].value + '_' + doc['name.keyword'].value"
        }
      }
    }
  }
}

"aggregations": {
  "duplicateCount": {
    "doc_count_error_upper_bound": 0,
    "sum_other_doc_count": 0,
    "buckets": [
      {
        "key": "[email protected]_SMITH",
        "doc_count": 1
      },
      {
        "key": "[email protected]_SMITH",
        "doc_count": 1
      }
    ]
  }
}