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Address matching: CASS, DPV and USPS address data

CASS-certified address-matching software standardizes an address and matches it to USPS's ZIP + 4 and City State Products to assign its ZIP + 4 and delivery point codes. DPV then confirms whether USPS delivers to the address, and LACSLink and SuiteLink supply converted addresses and missing suite numbers.

Updated November 5, 202692 sources

Questions

How do I know if USPS delivers to my address?

Delivery Point Validation, or DPV, is the USPS check in CASS-certified address-matching software that confirms whether USPS delivers to an address. An address on a phantom route, where USPS provides no delivery, gets DPV's enhanced return code R and only a 5-digit ZIP Code. DPV also flags vacant addresses, which were active in the past but no longer receive delivery. When someone creates a USPS.com account, usps.com checks the home address entered and says whether it is verified as a valid delivery address.

Is my address in the USPS database?

Every address USPS delivers to is in the Address Management System, USPS's national database of delivery addresses with their ZIP Code and ZIP + 4 code. Address-matching software checks one address with DPV, which tells whether a ZIP + 4 coded address is a known address record in USPS's delivery file. USPS's ZIP Code Lookup finds the ZIP Code for an address, but a result does not confirm that a person or company is there.

Why can't USPS verify my address?

Address-matching software may fail to verify an address that is missing an element, because it lacks the information to find the right ZIP + 4 match. On average, 8-10% of the addresses on a list cannot be ZIP + 4 coded or DPV confirmed by CASS-certified software. USPS's Address Element Correction service works on errors such as an incorrect street name, suffix or city name. On usps.com, an address it can't verify gets one of three messages: not found, so enter more information; a match for several more specific addresses, so choose one; or unable to verify, when some online services may not be available.

What is USPS address validation?

Delivery Point Validation, or DPV, is the USPS product that tells whether a ZIP + 4 coded address is a known address record in USPS's delivery file. DPV only checks: it adds no missing data and corrects no part of the address. USPS's Addresses API both validates and corrects address information, with data from the City State, ZIP + 4, Five-Digit ZIP, eLOT, DSF and LACSLink databases, for a price charged monthly by tier. Among USPS's shipping APIs, the Merchant Returns API checks a customer's address with the USPS Address Validation API.

What is USPS CASS certification?

CASS certification, from the Coding Accuracy Support System, is how USPS evaluates the accuracy of address-matching software. Any mailing claimed at an automation price must come from address lists matched and coded with CASS-certified methods. Only software and products can be CASS certified.

What is AEC and how does it work?

AEC, Address Element Correction, is a computerized address correction process for business mailers. USPS runs the mailer's address list through computer logic that corrects common misspellings and other errors. Addresses AEC cannot resolve can go through AEC II to delivery offices for review.

What is the turnaround time for AEC?

AEC returns a customer's file within 48 hours after accounting approves the AEC Processing Request Form. AEC II, which sends unresolved addresses to delivery units, works within a 30-, 60- or 90-day window the customer picks.

Is the AEC II service free?

No: AEC II has a set-up fee, paid through an Enterprise Payment System account or an approved credit card, and the minimum AEC service fee. The mailer also pays per record for each address that delivery unit employees resolve. As of October 4, 2026, Notice 123 prices AEC II at $59.00 for 1 to 100 records and $0.59 for each record over 100.

Will I need to complete CASS or MASS certification again for the Intelligent Mail barcode?

No, CASS applies to mail with the Intelligent Mail barcode, and there is no need to redo the certification. MASS has an annual certification requirement, and Intelligent Mail barcode certification is part of that process.

How it fits together

USPS keeps every delivery address in the Address Management System, the national database behind all its address correction tools. It offers address data to mailers as Address Information System products, raw database files such as the ZIP + 4 Product and the City State Product. Software must use both of those products to assign and check ZIP + 4 codes completely.

Address-matching software reads those files to standardize each address and match it to its ZIP + 4, delivery point and carrier route codes. Most companies that add ZIP + 4 codes to their lists buy CASS-certified software or hire a service bureau that runs it. CASS is USPS's certification of that software, and MASS extends it to the machines that read addresses on mail and apply barcodes. Developers can build software on USPS's own matching logic through the Address Matching System API.

Once an address has its ZIP + 4 code, CASS-certified software checks and completes it with the products that CASS certification includes:

  • DPV confirms that the address is a known USPS address record.
  • DSF2 can take DPV's place, making the same check and adding attributes such as vacant, business or seasonal.
  • LACSLink supplies addresses converted for the 911 emergency system.
  • SuiteLink adds a business's known suite number.
  • The Residential Delivery Indicator, whose certification is optional, tells whether an address is a business or a residence.

USPS calls all of these but the Residential Delivery Indicator its licensed products, and offers them through its Licensing Department. End users get the licensed products inside a CASS-certified product. When software still cannot match an address, USPS's Address Element Correction service corrects what it can, and AEC II sends the rest to delivery offices. County and municipal addressing authorities resolve differences between their address files and USPS's database through the County Project.

ZIP Codes and USPS address data

ZIP Codes are 5-digit codes that identify the Post Office or delivery station for every mailing address. A ZIP + 4 code adds four digits for the sector, such as a neighborhood, and the segment, such as a building, floor or street block. Two more digits, usually the last two of the street number, make the 11-digit delivery point code. It is the finest level to which mail can be sorted by its address. The Intelligent Mail barcode on a mailpiece encodes those two delivery point digits.

A complete address has every element needed to match the ZIP + 4 and City State Products exactly, down to its delivery point code. A standardized address is complete, uses USPS's official abbreviations for parts such as street suffixes, and is validated with those two products. Parts of streets with no possible delivery, such as those beside parks or railroad tracks, have no complete ZIP + 4 code. USPS's online ZIP Code Lookup finds the ZIP Code for one address, or all the ZIP Codes in a city.

USPS offers Address Information System products by annual subscription and issues them monthly through Electronic Product Fulfillment. They include these files:

  • The ZIP + 4 Product is the base reference that software reads to assign an address's ZIP + 4 code.
  • The City State Product lists ZIP Codes with their city and county names.
  • The Five-Digit ZIP Product adds ZIP Codes to mailing lists, with street detail for cities that have more than one ZIP Code.
  • The Carrier Route Product gives mailers carrier route codes for presort discounts.
  • The Delivery Statistics Product counts Post Office Boxes and business and residential deliveries for every ZIP Code.
  • The Z4CHANGE Product shows which ZIP + 4 codes were realigned in the past twelve months.
  • The ZIPMove Product helps software find ZIP + 4 codes after a realignment changed a city name or finance number. A finance number is the six-digit number that identifies a USPS installation for processing its financial data.
  • eLOT lets mailers sort mail in about the order a carrier cases it.
  • The AIS Viewer is an application that retrieves, views and prints ZIP Code information for all 50 states.
Must
The ZIP + 4® and City/State data must be updated by ZIP + 4 and City/State product users within 45 days of the USPS® release date (ref. USPS Domestic Mail Manual).

A user of the ZIP + 4 and City State Products must load each release within 45 days of USPS's release date.

ZIP Code

Also called ZIP, 5-digit ZIP Code, Zone Improvement Plan, Zone Improvement Program, ZONING IMPROVEMENT PLAN, Zone Improvement Plan Code

“a system of five-digit codes identifying the individual Post Office or metropolitan area delivery station associated with the address”

ZIP Code Lookup

Also called Look Up a ZIP Code

“An online application that allows a user to find a ZIP Code for a specific city or address, all ZIP Code numbers in a city, or all cities in a ZIP Code.”

non-deliverable

Also called ND

“Non-deliverable areas are areas to which the USPS does not deliver mail, such as vacant lots and land that borders railroad tracks.”

complete address

“An address that has all the address elements necessary to allow an exact match with the current USPS ZIP+4 and City State files to obtain the finest level of ZIP+4 and delivery point codes for the address. It is normally a standardized address and contains three required address lines in order from top to bottom: recipient line (personal name or organizational name), delivery address line (street address), and last line (city, state, and ZIP Code line). It can also include an optional attention line above the recipient line.”

ZIP+4

Also called ZIP+4 CODE

“An enhancement to the 5-digit ZIP Code that uses an additional four digits to represent the sector (a geographic area or neighborhood) and segment (a smaller unit such as a building, floor, street block) for an address within a 5-digit zone.”

delivery point

Also called DP

“A single mailbox or other place to which mail is delivered. A street address does not necessarily represent a single delivery point because a street address such as one for an apartment building may have several delivery points.”

standardized address

“An address that is complete, using official USPS abbreviations for elements such as directionals and street suffixes like ST or DR and state names, and validated with the ZIP+4 file and City State file.”

Address Management System

Also called AMS

“The national USPS database of every delivery address with its associated ZIP Code, ZIP+4 code, and city/state name that serves as the foundation of data for all address correction tools.”

Address Information System product

Also called AIS product

“A raw database file made available to customers to enhance address standardization, obtain detail address information, and correct address records.”

Address-matching software and certification

CASS tests address-matching software, and only software and products can be CASS certified. A manufacturer's certification works as a blanket certification for every user of its software, and each user needs its own only in certain situations. CASS-certified software must generate PS Form 3553, the CASS Summary Report, which the mailer signs to certify how the list was coded. NCOALink, an address correction service in Move Update, runs a CASS processing segment that gives each address its ZIP Code or ZIP + 4 code.

MASS certifies the machines that read addresses on mail and apply barcodes, such as multiline optical character readers. It tests whether each machine applies an accurate Intelligent Mail barcode. A machine's address-matching software must be CASS certified before anyone orders a MASS test deck for it. MASS certification lasts until the end of its annual period, from August 1 through July 31.

The Address Matching System API is USPS's own address-matching engine, offered through its Licensing Department. It includes the AIS products and every licensed product but DSF2. A manufacturer may build it into its own product under a direct license from USPS. Its users must still obtain CASS certification to receive automation discounts.

Must
Any mailing claimed at an automation price must be produced from address lists properly matched and coded with CASS-certified address matching methods.

A mailing at automation prices must come from address lists matched and coded with CASS-certified methods.

PS Form 3553

Also called CASS Summary Report

“This form may be generated as the output of address matching processing using CASS Certified™ software in conjunction with current USPS® address database files.”

Coding Accuracy Support System

Also called CASS, CASS software program, CASS certification process, Coding Accuracy Support System (CASS) certification

“provides hardware and software manufacturing, service bureaus, and commercial mailers a common measure by which to test the quality of address-matching software.”

Multi-line Accuracy Support System

Also called MASS, MULTILINE CODING ACCURACY SUPPORT SYSTEM, Multi-line Accuracy Support System (MASS) certification

“The MASS™ certification is a process similar to CASS but is designed for certification for Multiline Optical Character Readers (MLOCRs), Remote Video Encoding (RVE), and encoding stations to process address information and apply an accurate delivery point barcode (DPBC).”

Address Matching System Application Program Interface

Also called Address Matching System Application Programming Interface, AMS API, Address Matching System API

“AMS API is software used to develop address matching software. This software provides access to USPS® matching logic, which allows users to verify the accuracy of ZIP + 4® returns.”

Checking and completing an address

CASS certification requires the licensed products, and end users must use them in production.

ProductWhen the software uses itWhat it returns
DPVRight after CASS-certified software gives the address a 9-digit ZIP CodeY, D, S, N or blank; with the optional enhanced return codes, also R for an address on phantom route R777 or R779, which USPS doesn't deliver to
DSF2In place of DPV, also right after CASS-certified softwareThe same answers, plus attributes such as vacant or seasonal
LACSLinkWhen the ZIP + 4 match has an L in its LACS Status Indicator; also when the address matches a rural route or highway contract default, or no ZIP + 4 record, and its street is in LACSLink's street name tableThe converted address
SuiteLinkWhen a business address matches a street or highrise defaultThe suite number, when one is known
RDIOptionally, with CASS-certified ZIP + 4 softwareYes for a business or No for a residence

A ZIP + 4 match places an address within a range of addresses. DPV goes one step further and confirms the address as a known USPS address record. DSF2 processing is also one approved way to put mail in walk sequence when the mail isn't addressed with a simplified address. A simplified address, such as “Postal Customer”, takes the place of each name and address when identical mail goes to every customer on a route.

DPV and DSF2 also carry tables that flag particular kinds of address, such as these:

  • A drop is a single receptacle or drop site that serves several dwellings or businesses.
  • An internal drop address gets its mail through a drop address, not directly from USPS.
  • No secure location means the door is accessible, but a package will not be left there for security reasons.
  • Non-delivery days means mail is not delivered to the address on at least one day of the week.

Rural route and some city addresses are converted to city-style addresses so that emergency services can find them. The ZIP + 4 Product marks the records that may be converted with a LACS indicator. When LACSLink finds a converted address, CASS-certified software must return it. A suite number from SuiteLink may be left off the printed address, but to qualify for automation prices, the barcode on the mailpiece must include it.

Must
A Licensee or software developer writing an interface to the DPV product must first ensure the address list is processed through USPS CASS Certified software to obtain a 9-digit ZIP Code™ and a parsed address immediately prior to the validation process.

Software that connects to DPV must first run the address list through CASS-certified software, right before validation. That run gives each address its 9-digit ZIP Code and splits it into its parts.

DPV = Y

Also called Y

“Address was DPV® confirmed for both primary and (if present) secondary numbers”

drop site

Also called drop

“A drop is a single delivery point or receptacle that services multiple businesses/families.”

Internal Drop Address

Also called IDA

“Addresses that do not receive mail directly from the USPS, but are delivered to a drop address that services them.”

No Secure Location

Also called NSL

“Flag indicates door is accessible, but package will not be left due to security concerns”

Non-Delivery Days

Also called NDD

“Flag indicates mail delivery is not performed every day of the week”

Locatable Address Conversion System

Also called LACS, Locatable Address Conversion Service

“a product/system in a different USPS® product line that allows mailers to identify and convert a rural route address to a city-style address”

Locatable Address Conversion System Indicator

Also called LACS indicator, LACS Status Indicator

“The LACS indicator identifies addresses in the ZIP + 4® file that may be converted to new addresses.”

highrise default

Also called default highrise record

“A highrise default contains the building street address in the primary range field and spaces in the secondary range field.”

Licenses and data updates

USPS offers the licensed products through its Licensing Department. End users get this data inside a CASS-certified product, and standalone users get specially packaged data from a licensed service provider.

ProductWho may hold a license
DPVA CASS software manufacturer, or a company becoming one
DSF2A company that provides, or plans to provide, address verification and list processing services
LACSLinkInterface developers, interface distributors and end users, each under its own license
SuiteLinkA CASS software manufacturer or integrator, or a company becoming one, to develop an interface; a distributor, to pass the data on
AMS APIA manufacturer, under a direct license from USPS

USPS releases each licensed product monthly through Electronic Product Fulfillment, a secure USPS website, and only the two most recent releases can be downloaded. Customers open an account there with PS Form 5116, the Electronic Product Fulfillment Web Access Request Form. A DSF2 interface stops working once its data is more than 60 days past the product date. An interface to any other licensed product stops at 105 days.

USPS's National Customer Support Center in Memphis offers these products and services to help mailers improve and maintain address quality.

Must
The licensed products cannot be shipped outside of the United States.

A licensee must not ship the licensed products outside the United States.

PS Form 5116

Also called PS 5116, Electronic Product Fulfillment Web Access Request Form

“It is used to set up an account on the EPF website.”

Electronic Product Fulfillment

Also called EPF, Electronic Product Fulfillment (EPF) web site, Electronic Fulfillment Website

“A secure web-based application managed by the National Customer Support Center in Memphis TN that is used to post and receive Address Management and Address Information System products, including ACS fulfillment files.”

End User

“End Users are classified as customers receiving CASS Certified DPV data from a Licensed Service Provider.”

SuiteLink Interface Developer License

“The SuiteLink Interface Developer License authorizes the development of Interface Products to access the SuiteLink Product.”

SuiteLink Interface and Data Distributor License

“The SuiteLink Interface and Data Distributor License authorizes the right to distribute and market Interface Products and redistribute SuiteLink data to third parties.”

Correcting addresses

AEC works on addresses that CASS-certified software cannot match to a ZIP + 4 code. It uses Computer Logic Resolution, a program that runs evaluations and comparisons to correct insufficient addresses. AEC has an estimated correction return rate of 38%.

AEC II sends the records AEC cannot resolve to the post office that serves each address. There, delivery unit employees review the bad addresses and enter corrections, which USPS calls Delivery Force Knowledge. AEC II has an average correction rate of 51%. USPS introduced it to reduce undeliverable-as-addressed mail.

USPS may correct only the addresses a mailer presents, and may not supply other address information. Mailers prepay both services by credit card or through an Enterprise Payment System account.

The County Project is a free service for county and municipal addressing authorities, once a year. An authority sends its address file, and USPS returns the matched addresses standardized with their ZIP + 4 codes. Both sides then review the county codes and congressional districts that differ.

Address Element Correction

Also called AEC

“AEC is a process that turns problematic addresses into accurate addresses or identifies them as potentially undeliverable.”

Address Element Correction II

Also called AECII, AEC II Service

“AEC II is an enhancement to the existing AEC service, which identifies and corrects incomplete or inaccurate addresses using computer software. The addresses that cannot be resolved using AEC are submitted, via AEC II, to delivery offices for review and resolution.”

Computer Logic Resolution

Also called CLR

“CLR is a computer-based program that uses a variety of USPS programs and products to perform a series of evaluations and comparisons in an attempt to correct insufficient addresses.”

Delivery Force Knowledge

“Delivery Force Knowledge leverages the efforts of local delivery unit employees who review bad addresses and enter corrections into an AEC II electronic process for return to the submitting customer.”

County Project

“The County Project is for county and municipal addressing authorities working with AGT to improve address quality.”

What goes wrong

Software that does not return a LACSLink converted address can return only the 5-digit ZIP Code. That address does not qualify for automation discounts. A mailer that purposely uses the default ZIP + 4 code in place of SuiteLink's answer risks automation discounts on the whole mailing. An unreported change to CASS-certified software can get it decertified, and USPS can then rescind discounts mailers got with it, even retroactively.

DPV and DSF2 each include a table of artificially manufactured addresses, to catch lists that were not obtained legitimately. LACSLink includes one too. When an end user's list matches it, a DPV or LACSLink interface must stop processing that list. A DSF2 licensee may continue, but must notify USPS of the customer's name and address at once. A one-time restart code restores processing.

An address on a phantom route, where USPS does not deliver, gets DPV's enhanced return code R. It gets only its 5-digit ZIP Code, with no ZIP + 4 code or DPV confirmation. Highrise and rural route default matches stay eligible for automation prices, but many of them raise delivery costs.

USPS gives a new, moved, upgraded or reassembled MASS machine a 45-day courtesy period, in which its mail can qualify for automation rates before certification. A machine not certified by the end of that period becomes ineligible to submit mail at automation rates.

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