PO Box–Only ZIP Codes
The "Fast Lane" Answer
PO Box only ZIP Codes contain addresses where mailbox mail delivery is not offered. Each ZIP Code is designated with a “classification” indicator. Areas served only by PO Boxes receive a “P” classification.
Is there a list of ZIP Codes where the USPS doesn't deliver to physical addresses? Yes. The USPS keeps thorough
lists of just about everything. It's part of them being
a government organization so awesome.
The "Scenic Route" Answer
The USPS keeps track of more information than we normally give them credit for. So the fact that there's more than one kind of ZIP Code should come as no shock (but it does anyway). Here's a quick rundown of why there's more than one kind of ZIP Code.
ZIP Code Classifications
First, there are regular addresses. Addresses that receive mail at that physical location fall into this
category. For example, if the Caped Crusader can receive his shipments of new batarangs right at his front door,
Wayne Manor, 1007 Mountain Drive, Gotham meets this qualification. The USPS gives this kind of
address an "S" classification. The "S" is for "Standard." This is probably the category your home falls under.
Then there are addresses that are American by nationality, but not by locality. Military addresses run the gamut from ships at sea to embassies and bases around the world. Since ships are not stationary like normal addresses, and since military installations are often nestled amongst foreign soil, they get a special "M" (for "Military") classification. That identifies them as being reachable by the USPS, but requiring methods and delivery systems more akin to international shipping.
Here's a funny one: the "U" classification. It stands for "Unique," and its population includes companies, organizations, and other institutions that receive large quantities of mail. They're given their own "Unique" ZIP Code type.
And finally we come to PO Boxes. Areas served only by PO Boxes (mail is not delivered right to your doorstep) receive a "P" classification, mainly for how perturbed you're going to be trying to send mail to a physical address. Seriously though, the USPS classifies every ZIP Code that doesn't provide service to home and business locations with this label.
Getting Your Hands on the Data
Awesome. So there is a list. But you probably wanted to know how you could access and interface with it. Well, there are a number of ways to find out if a city contains "P" classification (or non-physical address) ZIP Codes.
If you just need to know if a location falls under the "P" category, that kind of information is the easiest to find. You can can do it now with our USPS postal address validator. Want to find an API that does it for you as you punch addresses in? That's a bit more specific. So is bulk address validation that runs a list of addresses at a time from an Excel spreadsheet or CSV file, to tell you what's a "P" ZIP Code and what's not.
For those last two, you're not likely to find a service that does just the ZIP Codes. Most providers package it together with things like geocoding, address standardization, validation and full 9 digit ZIP Codes. The good news is this: 5 digit ZIP Codes are the easy part.
To sum up: there is a list, it is accessible, and you can have even large lists checked to find out if your physical address are not directly serviced by the USPS. Places like "Zip-Codes" or "ZipInfo" can help you find a pre-generated list of ZIP Code types if that's what you need. If you're looking to find out if addresses you have on file fall under the "P" category (or any other ZIP Code type), we provide that information as part of our address validation services. Simply verify a postal address and we will let you know in the blink of an eye.