Priority vs. Express Mail: what's the difference? Ship a Package Now Learn More from the USPS About Priority Mail About Express Mail Learn About Flat Rate Boxes Priority Mail and Express Mail services are two of the most popular USPS mail classes. But what are the differences between the two services? And which one is right for you? Express Mail guarantees delivery by noon or 3:00 pm next-day to most U.S. locations. Priority Mail is delivered in an average of 2-3 days (without any guaranteed delivery times). Priority Mail is often delivered the next day if sent within the same postal zone. You can send both letters and packages using the Express Mail and Priority Mail services. Express Mail is automatically insured against loss for up to $100. Priority Mail does not include any insurance. You can add either USPS or Stamps.com insurance to any Express or Priority Mail package. Express Mail pricing begins at $10.40. Priority Mail can be sent for as little as $3.85. Both Priority Mail and Express Mail are available from the Mailing or Shipping tabs when you use Stamps.com.