Add or update a custom domain for email sending

curl --request PUT \
  --url https://api.open.cx/email/domains \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "domainName": "<string>"
}'

{
  "domainRecords": [
    {
      "type": "<string>",
      "name": "<string>",
      "value": "<string>",
      "ttl": "<string>",
      "status": "<string>"
    }
  ],
  "domainStatus": "pending"
}