Stamps.com supports a range of mail classes to fit your needs. Review the features and requirements below to select the right mail class for your shipment. First-Class Mail® 1-3 days delivery. Can be used for letters and packages up to 13 ounces only. Priority Mail® Average 2-3 days delivery. The economical choice for expedited delivery. Express Mail® Your fastest option. Next-day delivery to most destinations. Parcel Post® Ground Service - estimated 2-9 days delivery depending on destination. Send your packages economically. Media Mail™ (Book Rate) Ground Service - estimated 2-9 days delivery depending on destination. For shipments containing media materials only. Bound Printed Matter Ground Service - estimated 2-9 days delivery depending on destination. For shipments containing permanently-bound material up to 15 pounds only.