> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.freecustom.email/free-custom-email-api/v-1/custom-domains/add-a-custom-domain/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.freecustom.email/_mcp/server.

# Add a custom domain

POST https://api2.freecustom.email/v1/custom-domains
Content-Type: application/json

Adds a new custom domain to your account and returns the DNS records
you must configure at your registrar before verifying.

**Plan required:** Growth ($49/mo) or Enterprise ($149/mo).

**Workflow:**

1. `POST /v1/custom-domains` — add the domain, get DNS records.
2. Add the two DNS records (MX + TXT) at your registrar.
3. `POST /v1/custom-domains/{domain}/verify` — confirm propagation.
4. `POST /v1/inboxes` with any address `@yourdomain` — start receiving mail.

This call is **idempotent** — if the domain is already added it returns
the existing entry with `200` instead of `201`.

**Limits:** Maximum 10 custom domains per account.

Reference: https://docs.freecustom.email/free-custom-email-api/v-1/custom-domains/add-a-custom-domain

## Authentication

- `Authorization` header (bearer token, required) — Bearer authentication of the form `Bearer <token>`, where token is your auth token.

## Request

### Body (application/json)

This endpoint expects an object.

- `domain` (string, required)

## Response

### 200

OK

- `success` (boolean, required)
- `message` (string, required)
- `data` (V1CustomDomainsPostResponsesContentApplicationJsonSchemaData, required)

### 201

Created

- `success` (boolean, required)
- `message` (string, required)
- `data` (V1CustomDomainsPostResponsesContentApplicationJsonSchemaData, required)

## Errors

### 400 Bad Request Error

Bad Request

- `success` (boolean, required)
- `error` (string, required)
- `message` (string, required)

### 401 Unauthorized Error

Unauthorized

- `success` (boolean, required)
- `error` (string, required)
- `message` (string, required)

### 403 Forbidden Error

Forbidden

- `success` (boolean, required)
- `error` (string, required)
- `message` (string, required)
- `upgrade_url` (string, required)

### 429 Too Many Requests Error

Too Many Requests

- `success` (boolean, required)
- `error` (string, required)
- `message` (string, required)
- `upgrade_url` (string, required)
- `credits_url` (string, required)
- `hint` (string, required)

## Types

### V1CustomDomainsPostResponsesContentApplicationJsonSchemaData

- `domain` (string, required)
- `verified` (boolean, required)
- `mx_record` (string, required)
- `txt_record` (string, required)
- `added_at` (datetime, required)
- `dns_records` (list of V1CustomDomainsPostResponsesContentApplicationJsonSchemaDataDnsRecordsItems, required)
- `next_step` (string, required)

### V1CustomDomainsPostResponsesContentApplicationJsonSchemaDataDnsRecordsItems

- `type` (string, required)
- `hostname` (string, required)
- `value` (string, required)
- `priority` (string, required)
- `ttl` (string, required)

## Examples

### v1_custom-domains_Add a custom domain_example

**Request**

```json
{
  "domain": "mail.acme.com"
}
```

**Response**

```json
{
  "success": true,
  "message": "Domain already added.",
  "data": {
    "domain": "mail.acme.com",
    "verified": true,
    "mx_record": "mx.freecustom.email",
    "txt_record": "freecustomemail-verification=a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4",
    "added_at": "2026-01-15T10:00:00.000Z"
  }
}
```

**SDK Code**

```python v1_custom-domains_Add a custom domain_example
import requests

url = "https://api2.freecustom.email/v1/custom-domains"

payload = { "domain": "mail.acme.com" }
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript v1_custom-domains_Add a custom domain_example
const url = 'https://api2.freecustom.email/v1/custom-domains';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"domain":"mail.acme.com"}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go v1_custom-domains_Add a custom domain_example
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api2.freecustom.email/v1/custom-domains"

	payload := strings.NewReader("{\n  \"domain\": \"mail.acme.com\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby v1_custom-domains_Add a custom domain_example
require 'uri'
require 'net/http'

url = URI("https://api2.freecustom.email/v1/custom-domains")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"domain\": \"mail.acme.com\"\n}"

response = http.request(request)
puts response.read_body
```

```java v1_custom-domains_Add a custom domain_example
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api2.freecustom.email/v1/custom-domains")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"domain\": \"mail.acme.com\"\n}")
  .asString();
```

```php v1_custom-domains_Add a custom domain_example
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api2.freecustom.email/v1/custom-domains', [
  'body' => '{
  "domain": "mail.acme.com"
}',
  'headers' => [
    'Authorization' => 'Bearer <token>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp v1_custom-domains_Add a custom domain_example
using RestSharp;

var client = new RestClient("https://api2.freecustom.email/v1/custom-domains");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"domain\": \"mail.acme.com\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift v1_custom-domains_Add a custom domain_example
import Foundation

let headers = [
  "Authorization": "Bearer <token>",
  "Content-Type": "application/json"
]
let parameters = ["domain": "mail.acme.com"] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api2.freecustom.email/v1/custom-domains")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```

### v1_custom-domains_Add a custom domain_example

**Request**

```json
{
  "domain": "mail.acme.com"
}
```

**Response**

```json
{
  "success": true,
  "message": "Domain added. Configure the DNS records below, then call the verify endpoint.",
  "data": {
    "domain": "mail.acme.com",
    "verified": false,
    "mx_record": "mx.freecustom.email",
    "txt_record": "freecustomemail-verification=a1b2c3d4e5f6...",
    "added_at": "2026-03-11T12:00:00.000Z",
    "dns_records": [
      {
        "type": "MX",
        "hostname": "@",
        "value": "mx.freecustom.email",
        "priority": "10",
        "ttl": "Auto"
      },
      {
        "type": "TXT",
        "hostname": "@",
        "value": "freecustomemail-verification=a1b2c3d4e5f6...",
        "priority": "string",
        "ttl": "Auto"
      }
    ],
    "next_step": "POST /v1/custom-domains/mail.acme.com/verify"
  }
}
```

**SDK Code**

```python v1_custom-domains_Add a custom domain_example
import requests

url = "https://api2.freecustom.email/v1/custom-domains"

payload = { "domain": "mail.acme.com" }
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript v1_custom-domains_Add a custom domain_example
const url = 'https://api2.freecustom.email/v1/custom-domains';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: '{"domain":"mail.acme.com"}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go v1_custom-domains_Add a custom domain_example
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api2.freecustom.email/v1/custom-domains"

	payload := strings.NewReader("{\n  \"domain\": \"mail.acme.com\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby v1_custom-domains_Add a custom domain_example
require 'uri'
require 'net/http'

url = URI("https://api2.freecustom.email/v1/custom-domains")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"domain\": \"mail.acme.com\"\n}"

response = http.request(request)
puts response.read_body
```

```java v1_custom-domains_Add a custom domain_example
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api2.freecustom.email/v1/custom-domains")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"domain\": \"mail.acme.com\"\n}")
  .asString();
```

```php v1_custom-domains_Add a custom domain_example
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api2.freecustom.email/v1/custom-domains', [
  'body' => '{
  "domain": "mail.acme.com"
}',
  'headers' => [
    'Authorization' => 'Bearer <token>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp v1_custom-domains_Add a custom domain_example
using RestSharp;

var client = new RestClient("https://api2.freecustom.email/v1/custom-domains");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"domain\": \"mail.acme.com\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift v1_custom-domains_Add a custom domain_example
import Foundation

let headers = [
  "Authorization": "Bearer <token>",
  "Content-Type": "application/json"
]
let parameters = ["domain": "mail.acme.com"] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api2.freecustom.email/v1/custom-domains")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```