"registered email" meaning in English

{
  "forms": [
    {
      "form": "registered emails",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "registered email (countable and uncountable, plural registered emails)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "The electronic (email) equivalent of postal \"registered mail\", providing senders with a register enabling the location (delivery status and reading disposition) of their emails to be tracked."
      ],
      "id": "en-registered_email-en-noun-ILxaMD4i",
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "registered email"
}

{
  "forms": [
    {
      "form": "registered emails",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "registered email (countable and uncountable, plural registered emails)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English uncountable nouns"
      ],
      "glosses": [
        "The electronic (email) equivalent of postal \"registered mail\", providing senders with a register enabling the location (delivery status and reading disposition) of their emails to be tracked."
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "registered email"
}