identification requirements. While the Post Office permitted alternative designs for attached mailboxes and mail slots that met basic size and construction requirements, the same was not true for curbside mailboxes, which postal regulations required be in the form of the traditional dome-rectangular or 'tunnel-top' design first established in 1915. In 1978, seven years after the establishment of the restructured US Postal Service, postal authorities at last approved a "contemporary" mailbox specification for alternative designs. Currently, US curbside mailboxes are classified as (T) Traditional, (C) Contemporary, or (L) Locking. Traditional or Contemporary non-locking curbside mailboxes are approved in three sizes - No. 1, No. 2, or No. 3, measured by minimum interior dimensions. The largest acceptable curbside mailbox is the No. 3, which measures 22.81 inches long, 11 inches wide, and 15 inches in height (58 cm x 28 cm x 38 cm) at the peak. Locking mailbox designs that provide security for the recipient's incoming mail have fewer restrictions on shape and size, though designs with a slot for incoming mail must be at least 1.75 inches high by 10 inches wide. Residential locking mailboxes cannot require the postal carrier to have a key, by USPS Specifications. Therefore, no USPS approved residential locking mailbox has secure outgoing mail. Installation requirements vary from standard unlocked mailboxes: with locking mailboxes, the incoming mail slot must be 41"-45" above the roadside surface, and the front of the mailbox must be 6"-8" back from the curb. USPS specifications for all mailboxes mandate the same, except the placement of the 'incoming mail area' varies with a locking mailbox. Environmental conditions External or curbside letter boxes are not temperature-controlled, and this can sometimes be a concern for temperature-sensitive products such as pharmaceuticals, live plants or other organisms, or chocolate candies. Conditions can include high or low temperatures outside of the recommended storage conditions for certain products. For example, the USFDA found that the temperature in a steel mailbox painted black could reach 136 °F (58 °C) in full sun while the ambient air temperature was 101 °F (38 °C). Security There is a recommendation to have a lock on the letter box, if it is not built into a lockable door. Unlocked letter boxes are often used for identity theft, including the ordering of something valuable which is then stolen from the unlocked box. In the United States for example, by policy, the USPS will not