curl --request POST \
  --url https://api.coldsend.pro/api/public/v1/sender-accounts/{inbox_id}/test-email \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <api-key>' \
  --data '
{
  "recipient_email": "<string>"
}
'

{
  "success": true,
  "message": "<string>",
  "inbox_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "inbox_email": "<string>",
  "recipient_email": "<string>",
  "sent_at": "2023-11-07T05:31:56Z",
  "message_id": "<string>"
}