curl --request POST \
  --url https://api.aisa.one/apis/v1/agentmail/inboxes/{inbox_id}/messages/send \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "labels": [
    "<string>"
  ],
  "reply_to": "<string>",
  "to": "<string>",
  "cc": "<string>",
  "bcc": "<string>",
  "subject": "<string>",
  "text": "<string>",
  "html": "<string>",
  "attachments": [
    {
      "filename": "<string>",
      "content_type": "<string>",
      "content_id": "<string>",
      "content": "<string>",
      "url": "<string>"
    }
  ],
  "headers": {}
}
'

{
  "message_id": "<string>",
  "thread_id": "<string>"
}