Unique Identifier

Unique ID’s in the US

Are you looking for a unique value to identify addresses in the USA? Here, we cover the pros and cons of USPS data and look at alternatives

Are you looking for a unique value to identify addresses in the United States of America? The USPS is the postal authority here in the US and they are our first natural source to look to for a unique identifier. We will look at the pros and cons of USPS data and then look at our alternatives.

Benefits of a Unique Identifier

The main benefit of having a unique identifier is for detecting duplicates. When you verify and normalize an address to assign a unique identifier, 123 MAIN STREET Apt 12 and 123 MAIN ST # 12 both will resolve to the same address.

Additionally, addresses that get converted during the verification process with a CASS certified vendor like LACSLink and alias streets will also match.

Lastly, this unique identifier makes a good lookup key, because you can represent a full address by a single field. This is a simple way to hide the address behind another layer of data.

USPS Barcode

The USPS Barcode (also called Postnet Barcode) is a way to reduce an address down to 11 digits. These 11 digits are made up of the following:

Zip Code (5 digits)
Plus4 (4 digits)
Delivery Point (2 digits)

These 11 digits will resolve down to a single address. Incidentally, if you put this 11-digit number into a special font, you can get the barcode you often see on envelopes:



This is a quick and easy identifier and is available via almost all address verification solutions.


This code, while it will resolve to a unique address in almost all cases, does not guarantee uniqueness. The ZIP Code and Plus4 will narrow you down to a block of addresses. The 2 digits map to the last two digits of the house number or suite. In most cases, that will be good enough, but that is not enough for all cases. Here are some examples of cases where uniqueness cannot be achieved:

  1. Addresses with house number extensions:
    1332 Berry St vs 1332 1/2 Berry St
    450 Broadway Ave vs 450A Broadway Ave

  2. Addresses with long numbers where the last two digits can repeat:
    132250 Fairway Dr vs 133950 Fairway

Melissa Address Keys

Here at Melissa, we have our own version of unique identifiers. We will call these keys MAK for short. These are 10-digit unique identifiers that are guaranteed to be unique for all addresses. Since we are not using the ZIP Code, Plus4, Delivery Point system, we do not have the same issues with uniqueness. Additionally, MAK numbers apply not only to the US but to all major countries like Canada, United Kingdom, Germany, France, etc.

On top of MAK’s, we also have a value named Melissa Address Key Base (or BaseMAK for short). This value represents a unique key to the building of an address that contains suites or apartments. Using this value, you can quickly identify all addresses that belong to the same building. Here is an example:




660 S Figueroa St

Ste 1200



660 S Figueroa St      

Fl 21



660 S Figueroa St      

Ste 1450



If you are already using a Melissa product such as Address Object, Global Address, or Personator, you can already access these values by looking for the MelissaAddressKey and MelissaAddressKeyBase output fields.

How to Choose a Solution

Find the right address solution for your business by requesting a demonstration today.

At Melissa, we’ve leveraged 38 years of address verification expertise to give you the best possible products. Learn more from our collection of Address Experts articles.

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