Standard Class Mail: Holiday Arrangements When there are regional or local surges, or when there are equipment failures anywhere in the supply chain, it is more likely to be delayed. As the USPS prepares for a large increase in first class and package delivery, standard class direct mail suffers over the holiday season. During this time, many people have vacation or personal days off, which can cause delays if the mails aren't delivered during those times. Premium Class Mail: Delivery Delay Premium-class mail tends to be delivered in less busy times of the year, such as late fall through early spring. If your premium-class letter takes more than six months to reach its destination, you will receive another letter informing you of the delay. Express Class Mail: Worldwide Delivery Express Class Mail guarantees delivery within five business days after mailing. However, because these letters do not go through any sort of security screening process, they are easy to tamper with. If you require immediate confirmation that your letter has been received, consider choosing another form of delivery.