curl --request POST \
  --url https://api.mailchannels.net/tx/v1/send-async \
  --header 'Content-Type: application/json' \
  --header 'X-Api-Key: <x-api-key>' \
  --data '
{
  "content": [
    {
      "type": "<string>",
      "value": "<string>"
    }
  ],
  "from": {
    "email": "<string>",
    "name": "<string>"
  },
  "personalizations": [
    {
      "to": [
        {
          "email": "<string>",
          "name": "<string>"
        }
      ],
      "bcc": [
        {
          "email": "<string>",
          "name": "<string>"
        }
      ],
      "cc": [
        {
          "email": "<string>",
          "name": "<string>"
        }
      ],
      "dkim_domain": "<string>",
      "dkim_private_key": "<string>",
      "dkim_selector": "<string>",
      "dynamic_template_data": {},
      "headers": {},
      "subject": "<string>"
    }
  ],
  "subject": "<string>",
  "attachments": [
    {
      "content": "<string>",
      "filename": "<string>",
      "type": "<string>"
    }
  ],
  "campaign_id": "<string>",
  "dkim_domain": "<string>",
  "dkim_private_key": "<string>",
  "dkim_selector": "<string>",
  "headers": {},
  "tracking_settings": {
    "click_tracking": {
      "enable": false
    },
    "open_tracking": {
      "enable": false
    }
  },
  "transactional": true
}
'

{
  "queued_at": "2023-11-07T05:31:56Z",
  "request_id": "<string>"
}