What is a common feature of all types of Priority Mail boxes?

The common feature among all types of Priority Mail boxes is that tracking is included. This service allows senders and recipients to monitor the progress of their package as it travels through the postal system, providing peace of mind and accountability. Tracking is an essential aspect of the Priority Mail service, ensuring that customers can verify their shipment's status at any given time.

While flat rate shipping is a feature of some Priority Mail products, it does not apply to all types of boxes—only those marked as flat rate. The weight limit of 20 lbs pertains to certain services but does not universally apply to all Priority Mail boxes. Additionally, while Priority Mail often has similar delivery times, variations exist based on the specific service and destination, meaning it's not an absolute feature across all options.