With respect to database management, one of the questions we are most often asked concerns the difference between CASS and DSF2 address/mail processing. These services have grown more similar in recent years, but there are still important differences.


CASS – Coding Accuracy Support System – standardizes addresses and improves the accuracy of carrier route, five-digit ZIP, ZIP+4 and delivery point codes that appear on mail pieces. When mailers CASS certify their lists, they can become eligible for bulk mail discounts from the U.S. Postal Service (USPS).

In the past, applying these codes only required that mailing address fall within a valid address range. The address itself was not necessarily accurate. For example, ZIP+4 codes typically represent a range of 100 or fewer house numbers on a given street. While 100-199 Rollins Road may be assigned to ZIP+4 code 91311-7007, not all those house numbers are actual delivery points.

Since November 2, 2006, the USPS has determined that CASS-related discounts will only apply when the agency’s Delivery Point Validation (DPV) process confirms the primary number—or the first line—of the addresses. If the primary street number of an address cannot be confirmed with DPV, then no ZIP+4 code is assigned to the mail. Without a ZIP+4 code, the mail ceases to qualify for postal discounts. DPV is therefore now included with CASS processing.

CASS also integrates Locatable Address Conversion System service (LACSLink) which converts some PO Box and rural route addresses to city-style addresses and updates addresses that have been renumbered or renamed.

CASS processing software is graded by the USPS National Customer Support Center (NCSC), located in Memphis, Tennessee, by processing a test file. To be certified a 98.5% accuracy rate is required.


Prior to the November 2006 requirements added to CASS processing, DSF2 – Delivery Sequence File Second Generation – was the only fail-safe method of checking the accuracy of mailing addresses since CASS only determined if the address fell within a valid address range. But DSF2 continues to offer advantages that can make it a good choice.

In addition to all the processing and validation supplied with CASS, DSF2 also provides mailers with other important address attributes. It classifies an address as residential or business, identifies the delivery type—curb-side, door-slot, Neighborhood Delivery and Collection Box Unit (NDCBU) or central delivery—and flags seasonal and vacant addresses.

This information allows for more targeted mailings. For example, a company may want to send out a sample box of laundry detergent—with DSF2 they can target their mailing to residential addresses that do not have a door-slot mailbox since the sample would not fit through the slot.

DSF2 also appends codes that can be used to qualify for USPS Enhanced Carrier Route (ECR) Basic, High Density and Saturation postal discounts. These include Pseudo Delivery Sequence Numbers for walk sequence postal presort discounts and Enhanced Line of Travel codes (eLOT).

CASS and DSF2 have similarities and important differences. The choice is determined by the targeting required and the postal discounts that can be qualify for. In both cases, however, users will typically benefit from a significant reduction in undeliverable mail, speedier delivery and lower costs.

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