# Validate a reverse DNS record

## API Overview

Reverse DNS (formerly IP Whitelabel) allows mailbox providers to verify the sender of an email by performing a reverse DNS lookup upon receipt of the emails you send.

Reverse DNS is available for [dedicated IP addresses](/docs/sendgrid/ui/account-and-settings/dedicated-ip-addresses/) only.

When setting up reverse DNS, Twilio SendGrid will provide an A Record (address record) for you to add to your DNS records. The A Record maps your sending domain to a dedicated Twilio SendGrid IP address.

A Reverse DNS consists of a subdomain and domain that will be used to generate a reverse DNS record for a given IP address. Once Twilio SendGrid has verified that the appropriate A record for the IP address has been created, the appropriate reverse DNS record for the IP address is generated.

You can also manage your reverse DNS settings in the [Sender Authentication section of the Twilio SendGrid App](https://app.sendgrid.com/settings/sender_auth).

For more about Reverse DNS, see ["How to set up reverse DNS"](/docs/sendgrid/ui/account-and-settings/how-to-set-up-reverse-dns/) in the Twilio SendGrid documentation.

## Operation overview

```json
{"path":"https://api.sendgrid.com/v3/whitelabel/ips/{id}/validate","method":"post","servers":[{"url":"https://api.sendgrid.com","description":"for global users and subusers"},{"url":"https://api.eu.sendgrid.com","description":"for EU regional subusers"}]}
```

**This endpoint allows you to validate a reverse DNS record.**

Always check the `valid` property of the response’s `validation_results.a_record` object. This field will indicate whether it was possible to validate the reverse DNS record. If the `validation_results.a_record.valid` is `false`, this indicates only that Twilio SendGrid could not determine the validity your reverse DNS record — it may still be valid.

If validity couldn’t be determined, you can check the value of `validation_results.a_record.reason` to find out why.

You can retrieve the IDs associated with all your reverse DNS records using the "Retrieve all reverse DNS records" endpoint.

## Operation details

### Authentication

API Key

### Headers

```json
[{"in":"header","name":"Authorization","required":true,"default":"Bearer <<YOUR_API_KEY_HERE>>","schema":{"type":"string"}},{"name":"on-behalf-of","in":"header","description":"The `on-behalf-of` header allows you to make API calls from a parent account on behalf of the parent's Subusers or customer accounts. You will use the parent account's API key when using this header. When making a call on behalf of a customer account, the property value should be \"account-id\" followed by the customer account's ID (e.g., `on-behalf-of: account-id <account-id>`). When making a call on behalf of a Subuser, the property value should be the Subuser's username (e.g., `on-behalf-of: <subuser-username>`). See [**On Behalf Of**](/docs/sendgrid/api-reference/how-to-use-the-sendgrid-v3-api/on-behalf-of) for more information.","required":false,"schema":{"type":"string"},"refName":"#/components/parameters/OnBehalfOf","modelName":"__components_parameters_OnBehalfOf"}]
```

### Path parameters

```json
[{"name":"id","in":"path","description":"The ID of the reverse DNS record that you would like to validate.","required":true,"schema":{"type":"string"}}]
```

### Responses

```json
[{"responseCode":"200","schema":{"description":"","content":{"application/json":{"schema":{"type":"object","required":["id","valid","validation_results"],"properties":{"id":{"type":"integer","description":"The ID of the reverse DNS record."},"valid":{"type":"boolean","description":"Indicates if the reverse DNS record is valid.","enum":[true,false],"refName":"Valid","modelName":"Valid"},"validation_results":{"type":"object","description":"The specific results of the validation.","properties":{"a_record":{"type":"object","required":["valid","reason"],"properties":{"valid":{"type":"boolean","description":"Indicates if the reverse DNS record could be validated.","enum":[true,false],"refName":"Valid1","modelName":"Valid1"},"reason":{"description":"The reason the reverse DNS record could not be validated. Is `null` if the reverse DNS record was validated.","nullable":true,"type":"string"}}}}}}},"examples":{"response":{"value":{"id":123456,"valid":false,"validation_results":{"a_record":{"valid":false,"reason":"Failed to resolve A Record at o1.ptr4283.example.com: lookup o1.ptr4283.example.com on 192.168.0.10:53: no such host"}}}}}}}}},{"responseCode":"404","schema":{"description":"Unexpected error in API call. See HTTP response body for details.","content":{"application/json":{"schema":{"type":"object","required":["errors"],"properties":{"errors":{"type":"array","description":"The error messages for the failed validation.","items":{"type":"object","required":["message"],"properties":{"message":{"type":"string","description":"A message describing why the reverse DNS could not be validated."}}}}}},"examples":{"response":{"value":{"errors":[{"message":"Reverse DNS record not found."}]}}}}}}},{"responseCode":"500","schema":{"description":"","content":{"application/json":{"schema":{"type":"object","required":["errors"],"properties":{"errors":{"type":"array","description":"The error messages for the failed validation.","items":{"type":"object","required":["message"],"properties":{"message":{"type":"string","description":"A message describing why the IP whitelabel could not be validated."}}}}}},"examples":{"response":{"value":{"errors":[{"message":"internal error getting rDNS"}]}}}}}}}]
```

Validate a reverse DNS record

```js
const client = require("@sendgrid/client");
client.setApiKey(process.env.SENDGRID_API_KEY);

const id = "id";

const request = {
  url: `/v3/whitelabel/ips/${id}/validate`,
  method: "POST",
};

client
  .request(request)
  .then(([response, body]) => {
    console.log(response.statusCode);
    console.log(response.body);
  })
  .catch((error) => {
    console.error(error);
  });
```

```python
import os
from sendgrid import SendGridAPIClient


sg = SendGridAPIClient(os.environ.get("SENDGRID_API_KEY"))

id = "id"

response = sg.client.whitelabel.ips._(id).validate.post()

print(response.status_code)
print(response.body)
print(response.headers)
```

```csharp
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using SendGrid;

public class Program {
    public static async Task Main() {
        string apiKey = Environment.GetEnvironmentVariable("SENDGRID_API_KEY");
        var client = new SendGridClient(apiKey);

        var id = "id";

        var response = await client.RequestAsync(
            method: SendGridClient.Method.POST, urlPath: $"whitelabel/ips/{id}/validate");

        Console.WriteLine(response.StatusCode);
        Console.WriteLine(response.Body.ReadAsStringAsync().Result);
        Console.WriteLine(response.Headers.ToString());
    }
}
```

```java
import com.sendgrid.*;
import java.io.IOException;

public class Example {
    public static void main(String[] args) throws IOException {
        try {
            SendGrid sg = new SendGrid(System.getenv("SENDGRID_API_KEY"));
            Request request = new Request();
            request.setMethod(Method.POST);
            request.setEndpoint("/whitelabel/ips/id/validate");
            Response response = sg.api(request);
            System.out.println(response.getStatusCode());
            System.out.println(response.getBody());
            System.out.println(response.getHeaders());
        } catch (IOException ex) {
            throw ex;
        }
    }
}
```

```go
package main

import (
	"fmt"
	"github.com/sendgrid/sendgrid-go"
	"os"
)

func main() {
	apiKey := os.Getenv("SENDGRID_API_KEY")
	host := "https://api.sendgrid.com"
	request := sendgrid.GetRequest(apiKey, "/v3/whitelabel/ips/id/validate", host)
	request.Method = "POST"
	response, err := sendgrid.API(request)
	if err != nil {
		fmt.Println(err.Error())
		os.Exit(1)
	} else {
		fmt.Println(response.StatusCode)
		fmt.Println(response.Body)
		fmt.Println(response.Headers)
	}
}
```

```php
<?php
// Uncomment the next line if you're using a dependency loader (such as Composer) (recommended)
// require 'vendor/autoload.php';

// Uncomment next line if you're not using a dependency loader (such as Composer)
// require_once '<PATH TO>/sendgrid-php.php';

$apiKey = getenv("SENDGRID_API_KEY");
$sg = new \SendGrid($apiKey);
$id = "id";

try {
    $response = $sg->client
        ->whitelabel()
        ->ips()
        ->_($id)
        ->validate()
        ->post();
    print $response->statusCode() . "\n";
    print_r($response->headers());
    print $response->body() . "\n";
} catch (Exception $ex) {
    echo "Caught exception: " . $ex->getMessage();
}
```

```ruby
require 'sendgrid-ruby'
include SendGrid

sg = SendGrid::API.new(api_key: ENV['SENDGRID_API_KEY'])
id = "id"

response = sg.client.whitelabel.ips._(id).validate.post()
puts response.status_code
puts response.headers
puts response.body
```

```bash
curl -X POST "https://api.sendgrid.com/v3/whitelabel/ips/id/validate" \
--header "Authorization: Bearer $SENDGRID_API_KEY"
```