"mail relay" meaning in English

{
  "forms": [
    {
      "form": "mail relays",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "mail relay (plural mail relays)",
      "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"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Internet",
          "orig": "en:Internet",
          "parents": [
            "Computing",
            "Networking",
            "Technology",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A device or program that routes an e-mail to the correct destination."
      ],
      "id": "en-mail_relay-en-noun-mlvS8d7C",
      "links": [
        [
          "Internet",
          "Internet"
        ],
        [
          "device",
          "device"
        ],
        [
          "program",
          "program"
        ],
        [
          "route",
          "route"
        ],
        [
          "e-mail",
          "e-mail"
        ],
        [
          "correct",
          "correct"
        ],
        [
          "destination",
          "destination"
        ]
      ],
      "raw_glosses": [
        "(Internet) A device or program that routes an e-mail to the correct destination."
      ],
      "tags": [
        "Internet"
      ]
    }
  ],
  "word": "mail relay"
}

{
  "forms": [
    {
      "form": "mail relays",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "mail relay (plural mail relays)",
      "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",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Internet"
      ],
      "glosses": [
        "A device or program that routes an e-mail to the correct destination."
      ],
      "links": [
        [
          "Internet",
          "Internet"
        ],
        [
          "device",
          "device"
        ],
        [
          "program",
          "program"
        ],
        [
          "route",
          "route"
        ],
        [
          "e-mail",
          "e-mail"
        ],
        [
          "correct",
          "correct"
        ],
        [
          "destination",
          "destination"
        ]
      ],
      "raw_glosses": [
        "(Internet) A device or program that routes an e-mail to the correct destination."
      ],
      "tags": [
        "Internet"
      ]
    }
  ],
  "word": "mail relay"
}