• "ROYGBIV" is Copyrighted by Flickr user: SC Fiasco (Ed Siasoco) under the Creative Commons Attribution license.
  
  

Letters

• All letters are allowed to be mailed in a mailbox to another person. Letters can be categorized as greeting cards, a written letter or a postcard with a note written to another person.
  
  

Non-Hazardous Materials

• The post office does not allow hazardous materials to be mailed in a traditional mailbox. Dangerous liquids and materials cannot be mailed, but non-hazardous materials can be send via a traditional mailbox.
  
  

Non-Living Things

• The post office does not allow plants and animals that are living to be send through traditional mail. If you need to send a living item through the mail such as a pet or plant, you should contact your local post office branch for specific mailing instructions for that item. These types of items will also typically need to be dropped off in person at a post office rather than mailed in a traditional mailbox.
  
  

Medium-Sized Objects

• The post office has restrictions on how small and how large an object can be to be sent through traditional post. Items 1/4-inch thick or thinner are required to be rectangular and at least 3 1/2-by-5 inches in size. Objects can be no larger than 130 inches (combined length and girth) to be mailed. An "oversized" fee is assessed for items more than 108 inches (combined length and girth).
  
  

Lightweight Objects

• The maximum weight for objects that can be sent through the mail is 70 lbs.
  
  

Stamped Items

• All items mailed in a mailbox have to have the appropriate postage on them. It is a federal offense to place items in a person's mailbox, such as sales fliers, without paying postage. All items placed in a mailbox need to be put there by a U.S. Postal Service mail carrier.