USPS有具體規定，必須遵守郵箱時粘附到。應該使郵箱適合USPS列出的最新規則，最新是其中的最新規則USPS-STF-7Cdirective outlined in 2015.
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美國郵政總局規定的郵箱大小
Mailboxes in the US need to meet certain requirements.
According to USPS-STF-7C directive outlined in 2015, any curbside mailbox, whether rural or in a city,must be able to accommodate a test parcel that measures 7 inches high, 13 inches wide, and 16 inches deep.
鎖定郵箱還必須能夠通過3分鍾的測試，由此通常可用的工具，如Pry Bar等工具將無法訪問框中的郵件。具有鎖定機製的郵箱必須能夠在沒有需要鑰匙或代碼的郵件載體的情況下寄存在它們內部。
The directive set by the USPS sets out the minimum size requirements, but there are no maximum size requirements, so the homeowner can make a personal judgment as to how big their mailbox is, as long as it meets the minimum sizing.
Mail Amount
當考慮到哪個郵箱的大小獲得，請考慮您通常收到多少郵件以及您檢查郵箱的頻率。如果您經常訂購包裹，那麼一個較大的郵箱將更有用，但如果您不是一個大型在線購物者，而且大多隻收到賬單和銀行對陳述，那麼您將無需大郵箱。
If you check your mailbox regularly, then a minimum size mailbox will probably be adequate. However, if you frequently travel for work or have a situation where your mail is able to stack up in your mailbox, then you might want to consider a bigger box, so it doesn’t get jammed full.
能見度
您的郵箱的大小對於可見性至關重要，特別是如果您的財產非常農村。一個更大的郵箱將繪製更多的關注，幫助人們找到您的地址。
This is helpful not just for your mail carrier but also for anyone else, such as visiting family to find your home. A larger mailbox will allow you to display a larger street number on it, which will be easier to spot for passers-by. Most people, when trying to find an address, will use the numbers on people’s mailboxes to help them figure out where on the street they are.
Conformity
If you live in a residential area where there are lots of homes on a street, then you may want to take notice of the size of your neighbors’ mailboxes before you make a decision for your own.
If the whole street has got mailboxes of a similar size, then your mailbox might look awkward if it is significantly bigger than all the rest.
Mailbox Post Size
As well as the mailbox itself, there are guidelines for the mailbox post size, which the mailbox is supported. The Federal Highway Administration suggests that a pole must be strong enough to support the mailbox, but it should fall or bend if hit by a car so as to prevent injury to the public. Posts made from concrete or heavy metal are disallowed, and instead, 4×4 wood is recommended, or 2-inch diameter aluminum pipe.
The pole should be buried at a maximum of 2 feet in the ground and set back between 6 and 8 inches from the curb. The height of the post should be between 41 and 45 inches from ground level. This means that the bottom of the mailbox, or the mailbox opening, should sit at this distance from the ground.
Historic Mailbox Sizes
Since the United States Postal Service (USPS) began delivering rural mail in the late 1800s, mailbox size has been an ongoing issue. At first, as rural delivery was an experiment, customers made their own mailboxes out of old materials such as soapboxes or salvaged pieces of wood.
By the beginning of the 1900s, new rules were set out by a committee appointed by the Postmaster General regarding mailboxes. This stated mailboxes must be made of galvanized metal in order to protect mail from the weather and that they should measure approximately 6 inches by 8 inches by 16 inches.
1913年，介紹了包裹郵政，這意味著郵箱需要更大以容納包裹。郵政局長的一般建議尺寸更大，但這並沒有將行動作為要求作為必要的要求。
1916年，介紹了兩個隧道形郵箱，尺寸小，尺寸小，並且需要隻允許這些尺寸的郵箱安裝在農村路線上。
小尺寸為18½英寸長，6英寸寬，高7½英寸高。較大的尺寸為23½英寸長，寬11英寸，高14英寸。到1929年，由於包裹郵寄量的增加，這兩種尺寸的較小尺寸是停止的，並且較大的郵箱（稱為第2號）是新安裝唯一批準的框。
在整個20世紀50年代，這些法規接受了最小的變化，並在20世紀60年代，它們已更改為最小尺寸要求，而不是設定規模要求。圍繞材料的規定郵箱必須從也掉落，因為許多更便宜的郵箱通過塑料製成了這段時間。
最近，在2002年，改變了法規，其適用於農村和城市路邊郵箱的所有新安裝。這將郵箱的最小和最大尺寸尺寸詳細說明了大約18.5英寸至23英寸的長度，寬度為6至11英寸，高度為6至15英寸。
This has since been updated to regulations which state a mailbox must be able to accommodate a parcel measuring 7 inches tall, 13 inches wide, and 16 inches deep, but there is no set maximum dimension currently for mailboxes.
