Address Verification

USPS API and Address Validation Web Service

By 20 April 2024May 4th, 2024No Comments
usps api address validation service

Understanding USPS Address Verification, Validation and API Web Service

Any business with a large customer list or uses direct mail as a major channel for communication is bound to be familiar with the term address validation. If you haven’t already heard of address validation despite regularly sending direct mail, then it is high time to familiarize yourself with it.

The USPS API is synonymous with address validation in the US. Why? Because the primary purpose of the USPS validate address API is to validate addresses inside the US. It is, therefore, a necessary tool for all marketers, managers, and business owners who want to implement direct mail marketing campaigns.

usps api address validation service

But, to utilize the full potential of address validation USPS API businesses need to understand how it works. Only then can you understand how it can optimize your direct mail process. So, here we will try to portray a comprehensive picture of USPS API, address validation, and their nuances.

Understanding how an address validation process works is also critical in optimizing your direct mail process. This article discusses everything you need to know about the USPS address validation web service. So, pay close attention to every detail we discuss here if you wish to master the art of running a direct mail campaign using USPS API.

What is the USPS international address verification API?

The USPS API is not a single API or Application Programming Interface. It consists of a collection of public address validation APIs that serves different purposes. It also includes address lookup APIs provided by the USPS or United States Postal Service. With the help of a USPS address validation API, a developer can access the official address database maintained by the USPS.

The USPS address database contains over 160 million US postal addresses! In addition, it includes the complete ZIP code and city details. So, an address validation (or verification) API is nothing but an API or Application Programming Interface that enables you to validate an address.

What does this API do? It starts with verifying or validating postal addresses automatically saving you hours and oodles of money. Interestingly, most certified address validation API is capable of standardizing addresses based on USPS guidelines.

Another vital thing to note is that address validation APIs are highly integrable. You can have it connected to your website, database, and even CRM, among others. As a result, you can significantly enhance the quality of your database.

Address API Suites From USPS

The United States Postal Service offers three types of Address API suites. Listed below are these three address API suites and their purpose.

1. USPS validates address API/Standardization API
  • This API is used to verify or validate that an address is accurate and deliverable by the USPS.
  • Apart from validating the address, the API also standardizes the address to a format recognized by the USPS.
2. USPS ZIP Code Lookup API
  • The ZIP code lookup API provides you with the complete ZIP+4 code for an address you want.
3. USPS City State Lookup API

As you can see, each USPS address lookup API serves a different purpose such as address validation, standardization, and ZIP code/city lookup. Their functions range from address validation, address standardization, ZIP code API lookup, and more. However, using the USPS address suites may not be ideal for you, especially if you intend to use them often.

Verify Addresses with Geocoding API And PostGrid

PostGrid’s Geocoding API accepts both structured addresses and whole positions as its inputs.


USPS Address Database

As we mentioned above, the United States Postal Service maintains a massive address database for the entire country. There are about 160 million mailing addresses in this address database. The addresses in the database include all types of places, including business and residential addresses.

It even includes the post office box deliveries. Apart from this, the database also contains an extensive list of metadata points. For example, it provides information such as congressional district, time zone, county information, etc., of each delivery point.

Also Read: All You Need To Know About Web 2 Print API

Limited Access

The USPS’s address database is superior to any other address database in the country. It pans all over the US. Additionally, it also includes finer details that any private address database couldn’t even dream of. As you can imagine, the USPS does not let just about anyone access such precious data.

However, a few do have access to the official address database maintained by the USPS. But, even this access is provided only for them to view and check address validity.

CASS Certification

Those who can access the USPS address data like this include the official Address APIs and web forms. But, third-party USPS address verification service providers like PostGrid also enjoy the same privileges. Any third-party service provider that wants to access the USPS address database needs a CASS certification.

CASS is short for Coding Accuracy Support System. It is a certification program from USPS. A CASS certification allows third-party service providers like PostGrid to access the USPS address database. However, it is not easy to get a CASS certification.

Third parties have to abide by strict legal agreements and regulations. Only after complying with all the requirements can they become CASS-certified vendors. Furthermore, service providers like PostGrid are specialized tools that are built for broader applications aimed at businesses.

USPS Address Validation

Unlike what the name suggests, the USPS address verification API is not just limited to verifying an address. As we have mentioned before, the USPS address verification API also standardizes the addresses.

The USPS address validation web service changes the address format to align with the format defined by USPS. This makes the process of your direct mail much faster and minimizes the chance of delayed delivery.

How To Use USPS Address Verification

Using the USPS address verification API is quite easy, and you can follow the simple steps listed below for verifying an address.

Step 1

You need to compare the address in your hands against the address in the USPS official address database. So first, you must feed the address in your hand to the USPS address verification API. For example, let us consider the following address:
1408 B Imperial Suite 130
Provo PA

Step 2A

After you submit the address to the USPS address validation API web service, a response is generated. If the system finds an exact match for the address, then the response will be that the address is valid. The address validation process is then and there if the address you used is accurate.

Step 2B

If an exact match is not found in the USPS’s official address database, then the USPS API will try to correct it. In addition, the USPS verify address system will try to correct any minor errors by standardizing the address and comparing it against the USPS database.

But, this is only possible if the given address resembles an existing address in the USPS database. It means minor mistakes like errors in the casing, abbreviations, spelling, and other general typos. So, if the address is entirely made up, then the system generates a response that the address is invalid.

Coming back to the example that we had taken above, after standardization, the address comes out looking something like this:

Provo PA

Understanding USPS API Address Standardization And Verification

As you can see in the standardized address, some additional details have been added to the address. You can also see that the Suite in the address changes to STE (standard abbreviation). Furthermore, the system has also corrected the incorrect ZIP code.

It even provides you with a ZIP+4 code and a complete 9-digit ZIP code for the address you submitted. Once the standardization is done, comparing the new data against the USPS database becomes easy.

In other words, the standardization process is relatively more complex than the verification process. Therefore, you must ensure that the USPS address verification API you select has flexible standardization capability.

Luckily, most address verification APIs have some form of standardization capability. Hence, the USPS address verification API is often referred to as USPS address standardization API.

Additional Metadata From USPS API

After the USPS API standardizes and validates your address, it then enriches the addresses with additional metadata. You get the additional metadata along with the response from the USPS address verification API.

The additional metadata you get may vary depending on the address verification tool that you are using. However, you can generally expect to obtain the following details from the address verification API.

  • Carrier Route
  • ZIP+4 Code
  • Delivery point code
  • DPV confirmation indicator

Price of USPS API

A huge benefit of the US postal service address verification API is that it’s a free tool. After registering your account, you can use all the USPS postal address APIs free of cost. However, you must strictly follow the USPS terms of service while using their APIs.

The USPS terms of service can be a hindrance for many business applications of the API. We will discuss the limitations posed by USPS terms of service in detail as we proceed further. So, it is generally preferred by small businesses for optimizing their shipping and mailing purposes.

Limitations of USPS API

The USPS address verification may seem like a dream come true to marketers. However, it does come with a catch. There are certain limitations in using the USPS address verification APIs. So, you must know these limitations before you jump straight to coding.

The most common limitations of the USPS API fall under its Terms of Service, documentation, completeness, and uptime. As a long-term partner with USPS, PostGrid has closely examined its system and perfected a system of its own.

So, below we discuss some situations where you could run into some trouble when using the USPS API.

Challenges Due to USPS Terms of Service

The USPS web tools user guide explicitly states, “The Address Validation APIs can be used in conjunction with USPS SHIPPING OR MAILING SERVICES ONLY.”

According to the USPS terms of service, you can only use the API for shipping and mailing services. In other words, you can not use the USPS API for bulk address verification, cleansing your database, or managing your records.

Hence, you can only use the USPS address API for individual transactions where a customer or prospect enters their information into a website forum. But what happens if you do try to use the USPS API for something it is not meant to be? Like batch processing or database cleansing?

If you fail to comply with the USPS terms of service, it will immediately terminate the USPS API access. There will be no prior notice in such a case, and hence there is no telling when or how it might happen to you.

Most businesses with a relatively big target audience prefer to use a specialized address verification API like PostGrid. Using such specialized tools enables you to bulk verify addresses. It is ideal for businesses because it is much more convenient and takes a lot less time than the alternatives.

Challenges Due to Documentation & Support

As you know, the USPS API is not a specialized tool for business applications. They are best suited for individual use. Why do we say that the USPS API is not suited for business applications? Because there are certain requirements that an address verification API should meet for business applications, such as:

  • Tried and tested true example code obtained directly from the developers who created the address verification APIs.
  • An easily programmable code that can be easily copy-pasted and tweaked with a few lines. This way, the coding can be up and running in a matter of hours rather than days.
  • Access to flawless official SDKs in Python, iOS, JavaScript, and so on.
  • A responsive support system that can be easily accessed through different channels. It includes phone, email, and chat support.

Unfortunately, the USPS API does not deliver any of the requirements listed above. Hence, USPS API is not for you if you intend to use it for business applications.

USPS API Documentation

A considerable disadvantage of USPS international address verification APIs is that they have no example code. As a result, almost every business that tries out the USPS API believes that its documentation is weak at best. Furthermore, USPS does not provide SDKs for their APIs.

In other words, your business will have to code it from scratch, one line at a time. So basically, you have no shortcuts if you decide to use the USPS API. As a result, it takes extensive effort and time to put together a system, even if it only has minimum capabilities.

USPS API Support

Another big blow for businesses that rush into adopting USPS mail API for their website is discovering the lack of chat support. Now, you might think that you could make do with phone support. However, businesses that have gone ahead for phone support know that it is even more painful than testing it in production.

For one thing, you could end up listening to the half-minute song over and over for an hour or more after calling USPS support. But, even then, there is no guarantee of resolving the issue. So, be ready to resolve all the issues in-house if you still decide to go for a USPS API.

XML Based APIs

The USPS international address verification APIs are still based on XML, and as you may already know, they are incredibly outdated for today’s technology. Unfortunately, the XML format is so outdated that it can’t possibly keep up with your present needs or allow you to create innovative solutions.

Challenges Due to USPS API Uptime

We know that the United States Postal Service maintains the official address database of the country. So, it would make sense for the USPS API to be able to access them faster. However, that is not the case because the USPS API is notoriously famous for its inconsistent uptime.

It is one thing to get an address verification API for free and quite another to get one that is also reliable. When it comes to API solutions, you generally get what you pay for, which is true for USPS APIs. The USPS APIs are wildly famous for their regular downtime issues.

Challenges Due to Completeness

As we know, the primary purpose of the USPS database is to support the postal mail delivery system in the US. However, that does not mean that the USPS database contains every single postal address inside the country.

That being said, USPS still holds a monopoly over address data with 160 million addresses. It includes both business and home addresses. Unfortunately, they don’t have access to the addresses they don’t or can’t deliver.

Although not as extensive as USPS’s database, private postal service providers also keep their address database. Some of the major private deliveries in the US include FedEx, UPS, DHL, and Amazon. Each of these private postal service providers keeps its address database.
So, you can’t guarantee the validity of an address solely based on the USPS address database. However, checking the validity of addresses against the private database and USPS should give you a more concrete idea of an address’s validity.

Reliability of USPS API

The reliability of the USPS API is below-par at best. In addition, the USPS has poor quality documentation, and its terms of service are even more restrictive. Furthermore, using the solution for business purposes is next to impossible due to USPS APIs’ poor quality and flexibility.

However, on the bright side, you do have a lot of alternatives to USPS API with far-advanced and streamlined capabilities. So, if you are looking at the USPS API for business purposes, you should at least consider other alternatives.

Try USPS Validate Address API for Accurate Deliveries

Learn more about PostGrid Address Verification API, Reverse Geocoding API, and Address validation or Autocomplete.


Why You Should Consider Alternatives to USPS Address Verification API

The problem with the USPS address verification API is that it primarily focuses on putting the address data together. But, what it should be doing is delegate its attention towards how they share it. And this is where the third-party service providers come into the picture.

Fewer Restrictions

Third-party service providers such as PostGrid enable you to use the USPS address database more effectively. Furthermore, there are far fewer restrictions when it comes to using a third-party address validation API.

Unique Capabilities

When it comes to addressing validation APIs, each service provider has its specialized aspects. Therefore, the capabilities of the address validation tool will vary depending on the service provider. For example, PostGrid comes with additional features such as Address Autocomplete and Geocoding.

Therefore, an address validation API like PostGrid can be ideal for businesses with advanced marketing capabilities. Similarly, each third-party provider brings some unique capability to the table. It is up to the businesses to decide which one is best suited for their business and its requirements.

USPS Address Verification APIs And Its Alternatives

There are several third-party address validation APIs you can use as alternatives to the USPS API. However, finding the ideal one for your unique business can be challenging. Here, we list some of the most popular choices in address validation APIs. We also discuss the salient features of each of the service providers so you can get a comprehensive idea of what you are getting into.


Although the USPS international address verification API is far from perfect for business applications, it is still a well-rounded tool for personal or limited-scale use. Apart from this, there are some significant advantages you should consider using the USPS API:

Free Tool

The most significant selling point of the USPS address verification API is that it is free. Many businesses often choose to go ahead with the USPS API simply because it’s free. However, it usually does not work out for them if they need time-sensitive, high-volume address validation.

Data Quality

One of the main reasons to opt for the USPS address lookup API is its data quality. USPS maintains a high-quality database of addresses all across the US. Storing, updating, and tracking such a massive database is only possible for a service provider like USPS.

Web Interface For Address Validation

USPS is the only service provider that enables you to use Web Interface to validate addresses utterly free of cost. Although many service providers offer a limited number of free address lookups, none are free.

You can use the interface to enter an address easily, and the system will give you a heads-up if the address is valid. If not, the system will tell you that the address is invalid. However, you can only enter and validate one address at a time as it does not have bulk address verification capabilities.

Verdict: As long as your address validation requirement is not time-sensitive high volume, or system-critical, USPS API can work well for you. However, if your business requirements are more complex, it is best not to opt for a USPS API.

2. PostGrid

PostGrid is a well-rounded direct mail tool that is ideal for small to big-scale businesses. It offers a super-fast address validation API and web interface. In addition, they have a convenient bulk address verification process that can be carried out using nothing but a CSV file.

PostGrid also boasts several additional features that make it ideal for marketing purposes. This includes capabilities such as Geocoding and Address Autocomplete. Furthermore, PostGrid also has access to the official address database for international addresses. It includes addresses from countries like the UK, Canada, and Australia.

Complete Direct Mail Automation

The biggest advantage of PostGrid’s direct mail tool is that it can automate the entire direct mail process. So, everything from personalization, printing, and mailing of your direct mail can be automated via PostGrid. This is on top of a super-accurate address validation system that can process domestic and international addresses.


PostGrid has a geocoding feature that enables it to plot your address locations on a map. However, it does not have access to extensive address databases like Postal Offices. That being said, it can still process international addresses belonging to major countries like the US, UK, Canada, Australia, Europe etc.

Verdict: PostGrid comes equipped with a fully automated direct mail system that goes well beyond address validation USPS API. It is the ideal solution for small to big-scale businesses that want to optimize their direct mail operations.

PostGrid is perfect for companies that want to run advanced direct mail marketing campaigns. Its additional features such as Geocoding and Address Autocomplete enable you to target your audience better. As a result, you can run highly successful marketing campaigns and optimize all your direct mail processes.

3. Melissa Data

With a clientele that mostly consists of big enterprises, Melissa Data is a big name among address validation APIs. Due to the type of clients it serves, the company offers a much more advanced address validation which provides a lot of additional information.

Extensive Supplemental Information

Melissa Data offers an extensive range of supplemental information in addition to addressing data. It includes details such as email, validated addressee name, demographics, and even weather data. You get all these additional data, while the only data you give them is the address.

Easy to Use

Melissa Data has a straightforward interface that is super easy to use. You can easily validate your addresses without getting stuck in complicated procedures. Even their documentation is easily understandable as compared to USPS’s.

Additionally, it also has one of the best uptimes among address validation USPS APIs. It means you will never have an unresponsive or slow address validation process and therefore, highly reliable.

Verdict: Melissa Data is the best choice of USPS international address verification API if your business requires real in-depth information. It can provide you with a lot of additional detail, which you can use to target your audience better and categorize them.

4. Informatica

The most significant advantage of using Informatica as your address validation tool is its accuracy. The company provides reliable address validation services for both domestic and international addresses. In addition, it has access to extensive address data across 240 countries. Hence, Informatica is an ideal tool for global direct mail campaigns.

Accurate International Address Data

Data accuracy is the biggest selling point of Informatica. But, more importantly, Informatica can provide accurate address data for international addresses. The company’s ability to access super-accurate address data for international addresses can be helpful for businesses that deal with a lot of international clients.


Informatica also boasts an advanced geocoding feature that enables it to plot the address locations on a map. Interestingly, you can get the geocodes for even international addresses thanks to their accessibility to international address databases.

Verdict: Informatica is perfect for your business if you deal with a lot of international direct mail to numerous countries worldwide. It is also ideal for companies that want to run demographic-based marketing campaigns because of its geocoding ability.


The USPS API has some enticing features that are desirable in an address validation USPS API. Furthermore, there is no question about the data accuracy of the USPS address validation web service. However, USPS verifies the address is incapable of processing addresses in bulk and hence is not suitable for businesses.

On the other hand, third-party service providers like PostGrid are jam-packed with advanced features and capabilities.

Moreover, using a third-party service like PostGrid is the more reliable option as it requires minimum coding and quick-response support.

Using a system like PostGrid also gives you access to additional features like geocoding and Address Autocomplete. It enables you to automate the direct mail process and run advanced direct mail marketing campaigns.

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Understanding USPS API and Address Validation Web Service