An envelope's weight determines postage required.

The United States Postal Service, USPS, is the largest postal service in the world. According to the USPS, its mission is to "connect every American, every door, every business, everywhere through the simple act of delivering mail." The USPS functions independently from the rest of the government without the support of tax dollars through the sale of stamps, shipping materials and shipping services. Therefore, a stamp is the charge the sender pays to mail a letter. However, there are policies in place in case a letter is mailed without a stamp.

Forgot the Stamp

An item mailed without a stamp will be returned to the sender if a valid return address was written on the envelope. Validity of the sender's return address requires that a deliverable street number, street name and zip code are present on the envelope -- city and state help to confirm the zip code is correct. According to the United States Postal Service's policy, "It can take a few days for an unstamped item to be returned to the sender."

No Return Address

USPS will attempt to contact the recipient if unable to contact the sender. A postcard is mailed stating an item was sent to him without postage, and, for the cost of the correct postage, he can receive the letter. The recipient then must decide if he will pay the postage price to obtain the mail. If he does not want to pay or if the recipient cannot be reached, the letter is considered "dead" and is eventually destroyed.

Unreturned Letters

Letters that are determined by the USPS to have a value of less than $10 are destroyed after all valid attempts have been made. If the value of the letter or package is determined to be more than $10, the item is sent to a mail recovery center and held for up to six months, giving the sender or recipient an opportunity to try to claim the item. After six months at the mail recovery center, the item is put up for sale at an auction and any funds generated are credited to the USPS.

Customer Care Support

USPS provides customer support for individuals needing assistance regarding their missing items. Customers may contact customer service for help in tracking a letter or a package that was sent to a mail recovery center. Representatives are available by telephone or email. Additionally, the USPS has a frequently asked questions page for general customer service questions.