Are you saying that your physical mailbox is being used as the identity authentication instead rather than your personal number? > the closest tax office might

Are you saying that your physical mailbox is being used as the identity authentication instead rather than your personal number? > the closest tax office might be far away, so requiring the alternative process to be in-person would be impractical. Some countries require that the police visit you at home to verify that you live there, the closest police is hopefully not as far away as the closest tax office.