Here is an interesting problem I am facing... There are certain areas within the US where the USPS does not offer postal delivery to those addresses. One example here is my Zipcode 92067 which is "Rancho Santa Fe". All homes within the 92067 zip code can only accept regular postal mail when such mail is sent to ones PO box.

So, my question here is: where can I find a list of all zipcodes or for that matter zip4s which don't have rural delivery.

Thanks in advance!

Based upon the data from Jeffery I created the following dataset, mapped and plotted the results based on those zipcodes. Here are the results of that work: https://www.google.com/fusiontables/DataSource?snapid=S441148K1ew


2 Answers 2


Let me point out first that there are also addresses that the US Post Office doesn't deliver to at all. Not even to a common mail receptacle or group of mailboxes. Certainly anyone can get a PO box at the nearest Post Office. Many times, a remote, or extremely rural address will still be serviced by UPS or Fedex.

The USPS designates each ZIP Code with a "type" to help them sort mail more quickly. The "type" can be any of the following:

S - Standard - A "standard" ZIP Code is what most people think of when they talk about ZIP Codes - essentially a town, city, or a division of a city that has mail service.

P - PO Box Only - Rural towns, groups of towns, or even high-growth areas of cities are given a "PO Box Only" ZIP Code type.

U - Unique - Companies, organizations, and institutions that receive large quantities of mail are given a "unique" ZIP Code type.

M - Military - Military bases overseas - and often vessels and ships - are given a "military" ZIP Code type.

It sounds like you want to find the ZIP Codes with "P" type, meaning they service a PO Box only. There are many ZIP Code database services. Ones that I have worked with in the past is zip-codes or zipinfo. They offer A LOT of metadata about ZIP Codes.

Keep in mind, that a ZIP Code can span multiple cities, counties, and even states. Yes, there are some ZIP codes that exist in multiple states. That is because a ZIP code is not a physical boundary but a postal route designed with convenience and efficiency in mind. If there is a remote mountain road that is only accessible from a small town in Alabama but that road crosses over into Mississippi, the addresses on that road will be serviced by the post office (or ZIP Code) that is in Alabama.

Because of this seeming inconsistency, a 5 digit ZIP Code is not as valuable as a 9 digit (or ZIP+4) code. The ZIP+4 code designates a specific area, typically a city block or grouping of houses and so is much more precise. There are 42k unique ZIP Codes currently in use and that means that the possible number of ZIP+4 codes is 420 Million. Since there are only 300 Million mailing address in the US, that still leaves some room for growth.

To summarize, ZIP codes are USPS delivery areas, not necessarily matching any political borders. ZIP+4 codes are block-level delivery areas and in order to get a ZIP+4 for any given address you must process an address through an address verification service. (I work for one called SmartyStreets.)

  • Thanks Jeffrey - I am well aware of the classification elements you mentioned for zipcodes although I was not aware of the P classification so thanks for that. Also it seems there is another Z classification as well. See: zip-codes.com/zip-code/92067/zip-code-92067.asp Seeing that you have the data there, would you mind doing a resort on the columns related to both classification = 9 and city type = Z and let me know how many results come up? Oh, and one slight correction to your 300 Million remark - that number seems to high because there are only about 130 Mil residentials. Commented Mar 27, 2012 at 2:54
  • zip-codes actually designates eight different ZIP-code types. (zip-codes.com/zip_database_fields.asp#citytype). It looks like they have added a few more classification system than the USPS actually uses. The ZIP Code file that I have uses the 4 ZIP Types that I mentioned: "S", "P", "U", and "M". I checked the August 2011 database and there are 12,665 ZIP codes that are PO Box only. I'd be happy to get this list to you. How do I do that? Also, if the 130Million residential addresses is a good number, then 300Million total deliverable addresses would certainly be a little high.
    – Jeffrey
    Commented Mar 27, 2012 at 14:34
  • if you send me the file I will go ahead and make it publicly available to do so go ahead and send an email to chris@ + my username here. Commented Mar 27, 2012 at 21:39
  • I'd like to get a copy of the file that contains all the PO Box zip codes in the USA. The link by the poster is dead. Know of another source?
    – RonC
    Commented Nov 25, 2020 at 22:29
  • The current Zip Code list is available for download on this page: account.smartystreets.com/#tools. (you'll need at least a free account)
    – Jeffrey
    Commented Jan 22, 2021 at 21:55

Just to clarify,

It looks like you are looking at the "City Type" field which is different from the "Classification Code" which is where you would find the fields you are looking for.


  • Agreed. I believe it is the City Type that he needs. I sent him a data file.
    – Jeffrey
    Commented Mar 28, 2012 at 5:53
  • Mapping the data as we speak Commented Mar 28, 2012 at 7:15

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