usps priority mail usa USPS Priority Mail is a fast and reliable shipping option for domestic orders within the United States. This service guarantees delivery within 1 to 3 business days, depending on the destination, and includes tracking and insurance coverage. Priority Mail is commonly used for both personal and business shipments, offering a balance of speed and affordability. It’s ideal for e-commerce businesses looking for timely delivery without the higher cost of express services. This service also includes free package pickup and flat-rate options for certain package sizes.