curl --request POST \
  --url https://api.sentvia.ai/v1/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "inbox_id": "<string>",
  "to": [
    "<string>"
  ],
  "subject": "<string>",
  "cc": [
    "<string>"
  ],
  "bcc": [
    "<string>"
  ],
  "text": "<string>",
  "html": "<string>",
  "in_reply_to": "<string>",
  "references": [
    "<string>"
  ],
  "client_id": "<string>",
  "attachments": [
    {
      "filename": "<string>",
      "content_type": "<string>",
      "content_base64": "<string>"
    }
  ]
}
'

{
  "id": "<string>",
  "thread_id": "<string>",
  "message_id": "<string>",
  "ses_message_id": "<string>",
  "idempotent": true
}