The DPV database is included in ZP4 to allow enhanced address validation beyond what's possible when only the ZIP + 4® database is used.
Without DPV, the ZIP + 4 database is only capable of confirming whether addresses fall within the "low to high" address ranges specified in ZIP + 4 records. For example, "100 to 198 (even) MAPLE AVE" is a typical house number range listed in the ZIP + 4 database, and any even house number in that range will match that ZIP + 4 record, whether or not the address is a valid Postal Service delivery point.
With DPV, ZP4 can confirm whether any individual address is a valid delivery point, regardless of what the ZIP + 4 database range implies. For example, only three addresses might actually exist in a given range like "100 to 198 (even)". Using DPV, ZP4 will validate the three known addresses and reject any other address in the range.
In other words, with just a ZIP + 4 database, you can only determine a candidate ZIP + 4 for an address, but since ZP4 includes both ZIP + 4 and DPV databases, you can also determine whether the address is a valid delivery point and produce valid ZIP + 4 codes.
In addition to allowing ZP4 to return a "yes/no" indication for any specific mailing address, DPV also allows ZP4 to detect if an address is a Commercial Mail Receiving Agency (a "mail drop" that rents mail boxes), if an address is vacant, if the mail carrier can't knock on a door (for example, the building can't be physically accessed due to a long driveway or gated residence), if the address is known but does not yet receive mail (for example, new construction that does not yet have a mail box), if a street address is actually a PO box at a post office, and if the address has no security (for example, mail carriers can't leave packages due to security concerns, or the address is a business sometimes closed on delivery days, or a storefront with no mail receptacle).
Postal Service licensing prohibits using DPV for the manufacture of address lists. A "violation" will occur if ZP4 detects DPV is being used to generate address lists, and subsequent DPV output will be suppressed. Violation monitoring and enforcement is a requirement of the Postal Service. Semaphore Corporation is required to notify the Postal Service of your name and address upon a violation. If you repeatedly generate DPV violations, the Postal Service will prohibit you from continuing to use the DPV system.
In December 2001, ZP4 became the first product ever certified by the Postal Service for DPV processing. DPV, LACSLink®, and SuiteLink® are required to determine the proper CASS™ generated ZIP + 4 code for an address.
ZP4 is also the first product ever certified by the Postal Service for the super-fast DirectDPV form of delivery point validation.