First class is the top grade of regular mail. Use first-class stamps on letters, postcards and small packages. The mail will arrive more quickly than second- or third-class mail, which are for bulky items such as books. Use parcel post to send packages up to 70 pounds and up to 130 inches as of 2010 when you add the length to the circumference at the widest girth. Parcel post packages are delivered in a truck instead of by the mail carrier. First class and parcel post are charged by weight, distance and sometimes shape.
The first five digits of a ZIP code tell postal workers what postal facility can deliver the addressed mail. The mail is forwarded to that facility and workers there deliver it to the addressee. In 1981, four digits were added to ZIP codes. The first two pinpoint a geographic division within the service territory of a post office. This might be a rural route or a county. The last two digits indicate blocks, apartment buildings, large firms or buildings where mail is to be delivered.
Registered mail is held under tighter security than regular mail, and the contents are insured up to $25,000. You are given documentation to track the date and time of delivery online.
The fastest type of first-class mail is Express Mail. The postal service guarantees overnight delivery within the United States. Deliveries are made every day of the week, including holidays and weekends, and packages can be tracked online. The post office delivers Express Mail to mailboxes and post office boxes or you can request a signature to prove delivery.