What should a mailer ensure about the address on a package?

The essential requirement for the address on a package is that it must be visible and legible. This ensures that postal workers can easily read the address and deliver the package to the correct destination without confusion or delay. A clear and well-placed address minimizes the risk of misdelivery and increases the efficiency of the mail processing system.

While handwriting the address can be acceptable, it's not a strict requirement, hence the option would not be the best choice. Similarly, using blue ink is not a universal requirement for mailing addresses; any dark, clear ink typically suffices. The address also needs to be placed in a standardized position on the package rather than anywhere, as proper formatting aids in quick recognition and processing during shipping.