Address Verification

ZIP Code Validation

By 31 March 2024April 28th, 2024No Comments
zip code validation

US ZIP Code Validation - Validate using Zip Code Validation API

ZIP Code validation has now become a necessary part of sending direct mail pieces for businesses. Different businesses may have different purposes and goals for sending direct mail. For example, some use direct mail to send bills or invoices, and others may use it for direct mail marketing, and so on.

zip code validation

Whatever the purpose or goal of sending direct mail, businesses inevitably need a ZIP Code validation capability. Why? Because direct mail is unlike digital communication channels like text messages or emails. They require feasible resources such as paper, ink, envelopes, etc.

Delivering direct mail to the wrong address or being unable to deliver mail can cost you valuable time and money. You may also have to resend the undelivered mail, which can further lead to a waste of resources and unnecessary loss. It also means you will have to restart all over again.

Today, we will discuss everything you need to know about ZIP code verification. First, the article will take you through the significance of postal code verification for direct mail. Through the same, we will also explain how you can verify ZIP code with USPS.

So, keep reading to know more.

What Does a Valid Zip Code Mean?

ZIP code verification or ZIP code validation is the process of checking whether a postal mail address is accurate and deliverable. The process involves checking whether the given ZIP code matches the location in the address. A valid ZIP code must meet three criteria, and they are as follows.

  • The Given ZIP code must have a match in the USPS's official address database.
  • The ZIP code in the address must correspond accurately with the city or town in the address.
  • The ZIP code must be in the correct or standardized format, including the ZIP+4 code.

Why Should You Validate ZIP Codes Using API?

Validating ZIP codes using API before sending direct mail has already become the norm for many companies. This includes all sorts of direct mail assets, including letters, advertisements, product catalogs, and more. So the short answer to why you should validate ZIP codes is to enhance direct mail deliverability.

But, postal code verification does so much more than enhance the deliverability rate of your direct mail. Some of the most significant effects or advantages of ZIP code validation often go unnoticed or underappreciated. So, below we have listed some of the significant benefits of ZIP code verification.

Minimize Return Mail

We know that using a ZIP code verification lets you enhance the deliverability rate. Now, as the deliverability rate goes up, the number of return mails goes down. It means that you can successfully avoid wasting resources like paper, ink, etc., on your direct mail.

Minimize Postage Costs

Suppose you send out 1000 direct mail postcards and 10 of them are returned to you. In this case, you are needlessly spending money on the postage charges of the 10 returned postcards. These returned mail did not serve any purpose. It merely ended up in the shredder wasting your valuable resources.

Minimize Shipping Time

The ZIP code validation helps you get a complete 9-digit ZIP code for your addresses. Providing a full 9-digit ZIP code makes it easier for USPS to sort and mail your direct mail. As a result, you can avoid unnecessary delays in the delivery process and minimize the shipping time.

Minimize Wastage

As you may have already noticed, US ZIP code format validation is a great way to minimize wastage. However, there are different kinds of wastage that are avoidable by employing a ZIP code verification process. Some of the significant wastages that are avoidable via ZIP code validation are as follows.

Resource Wastage: Resource wastage includes all material resources that go into personalizing, printing, and delivering a mail piece. Paper, ink, and glue are the most apparent resource wastage you can avoid with a ZIP code validation. This wastage may seem minute if you look at them individually. However, if you consider bulk mail, such wastage can add up to a significant amount.

Time Wastage: Processing direct mail can be highly time-consuming. It is especially true if you don't use an automated direct mail system like PostGrid. All the time you take to personalize, print, and mail a letter or postcard goes to waste when it gets returned to you. By minimizing the return rate, ZIP code address validation ensures accurate and fast delivery of your direct mail.

Money Wastage: As you know, wasting resources ultimately leads to money wastage. For example, printing direct mail requires high-quality paper and ink, and they do not come cheap. Furthermore, you also end up spending money on postage charges. To top it all off, once you get the address of a returned mail verified, you would have to spend more money on resending the mailer.

How Can You Tell if a ZIP Code is Incorrect?

ZIP codes, as you know, consist of numbers. Therefore, there is no way of determining whether a ZIP code is valid or not just by looking at it. For example, let's assume you have a ZIP code on an address. But the ZIP code doesn't accurately correspond to the correct city or town mentioned in the address.

In other words, the ZIP code does not match the city or town mentioned in the same address. As far as USPS is concerned, the address data provided in the mailer contradicts itself, the USPS can not deliver it. As a result, the mailer gets returned to the sender.

So, how does the ZIP code validation system successfully determine whether the ZIP code is valid or not? The process behind this is more straightforward than you might think.

To understand the process better, let us take the example of an incorrect ZIP code.

13 Shell Street
Drexel Hill, PA 19025

Step 1: Look For The ZIP+4 Code

ZIP+4 codes are four-digit codes at the end of the standard five-digit ZIP code. The first thing you need to look for in a ZIP code is the ZIP+4 code. Why? Because a ZIP+4 code defines the exact location of the delivery address. It is less likely that a ZIP code is invalid if it contains a complete ZIP+4 code.

However, there is still a good chance that the ZIP code has an accidental error due to manual processing. This is why most businesses now prefer to use an automated system like  PostGrid for printing their mailers.  

Step 2: Check Whether The ZIP Code Matches The City or Town

The next step is to match the ZIP code against the city or town in the given address. Reusing the help of the example, the address provided above lists the location of the city as Derex Hill, PA. However, upon checking the ZIP code, you can find that 19025 corresponds to Montgomery, PA. 

If you look up the ZIP code for Derex Hill online, you can see that the city's actual ZIP code is 19026. And even though we can infer that this is a common typo by examining it, there is no way we can know this for sure. 

Obviously, the USPS does not work on guesswork either. Hence, the USPS returns letters with such addresses or mismatched ZIP codes. However, you can easily avoid these circumstances if you verify the ZIP code with USPS.

What Happens to Addresses After ZIP Code Verification?

Now, we know how you can tell if a ZIP code is valid or not. Let's see what happens to the address after you validate its ZIP code. Given below is how the address we've taken as an example will look after ZIP code verification. 

13 Shell St
Drexel Hill PA 19026-1408

As you can see, the corrected address has a full ZIP+4 code. The ZIP+4 code alone clarifies the exact delivery location of the mailer. 

Address Correction Charges & Special Mail Rates

Having a valid ZIP+4 code on the mailer also means that you can avoid address correction charges from USPS. It is crucial because USPS can charge up to $40 to change an address. And sometimes, the change isn't even made on the address.

Avoiding huge address correction charges is not the only monetary benefit you get from ZIP code validation. There is a chance that you qualify for special mailing rates simply by using the ZIP+4 code. However, this is unlikely to apply to your business if it only sends out a minimal number of mailers.

Also Read: Business Address Verification and Validation

What Are The Tools You Can Use For ZIP Code Validation?

There are several tools available that let you verify zip codes with USPS address databases. However, businesses often send out bulk mail. You can even find free tools available that you can use for ZIP code verification API.

USPS Postal Code Verification

USPS offers Address Verification APIs. You can either make use of their full address verification API or use a simple ZIP code lookup. USPS even has a web interface through which you can verify ZIP codes with USPS. However, there is one major catch in using USPS's free ZIP code verification.

Even though USPS offers a free solution, it may not be the best choice for you if your business requires sending bulk postal mails. It is true even for their address validation API. Hence, most companies often go for a more advanced third-party solution.


PostGrid is a third-party direct mail solution that businesses prefer when it comes to ZIP code validation. The popularity of PostGrid for business applications is understandable considering its features and capabilities.

PostGrid lets you bulk verify entire addresses and not just the ZIP code. All you need is a CSV file of your address data. You can use their API or the web interface for verification. You also get to automate the entire direct mail process, including personalization, printing, and mailing.

With automation, you don't have to worry about any manual errors or typos. As a result, you can minimize the return rate and ensure optimized execution of your direct mail process.


ZIP code validation is now a necessity for any business that sends regular direct mail to its customers. It saves you valuable time and money you spend on your direct mail campaigns. In addition to this, you can also avoid wastage of resources as ZIP code verification significantly boosts the deliverability rate.

Although USPS offers a free tool to verify zip codes, it is not practical for business applications. The main reason for not using USPS's free tolls is that it does not support bulk verification. On the other hand, third-party solutions like PostGrid are ideal for businesses.

PostGrid provides superior ZIP code verification capabilities. Furthermore, it provides a single fully automated solution for direct mail. As a result, you can significantly minimize the time you spend on the direct mail process and get the best result.

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