curl --request POST \
  --url https://smtp.sendmux.ai/api/v1/emails/send/batch \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "messages": [
    {
      "from": {
        "email": "user@example.com",
        "name": "John Smith"
      },
      "to": {
        "email": "user@example.com",
        "name": "John Smith"
      },
      "subject": "Welcome to SendMux",
      "html_body": "<string>",
      "text_body": "<string>",
      "reply_to": {
        "email": "user@example.com",
        "name": "John Smith"
      },
      "return_path": "jsmith@example.com",
      "cc": [
        {
          "email": "jsmith@example.com",
          "name": "<string>"
        }
      ],
      "bcc": [
        {
          "email": "jsmith@example.com",
          "name": "<string>"
        }
      ],
      "custom_headers": {},
      "attachments": [
        {
          "filename": "invoice.pdf",
          "content": "<string>",
          "type": "application/pdf",
          "encoding": "base64"
        }
      ],
      "idempotency_key": "<string>"
    }
  ]
}
'

{
  "ok": true,
  "data": {
    "results": [
      {
        "index": 123,
        "message_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
        "status": "queued",
        "error": {
          "code": "validation_error",
          "message": "<string>",
          "param": "<string>",
          "doc_url": "<string>"
        }
      }
    ],
    "summary": {
      "total": 123,
      "queued": 123,
      "failed": 123
    }
  },
  "meta": {
    "request_id": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx"
  }
}