Express mail provides shipment of letters, documents, and other mailed items. Express mail collected during the day will be processed the same day. On days before weekends or holidays unless the sender has verified that someone will be available to accept it and work on it during the weekend or holiday. This is the most expensive service. Priority Mail is used when the speed of express mail is not needed, but preferential handling is desired.
Priority mail offers faster delivery at a less expensive rate.
Priority mail is first class mail not exceeding 70 pounds and 108 inches in length and girth combined. At the option of the mailer, any mail may be sent priority mail. There is no minimum weight limitation 3. First Class Mail can be any mailed matter. If your first class mail is not letter size, make sure to mark it first class , otherwise it will be mailed at the lowest rate.