FAQ What is DPV? Delivery Point Verification (DPV) is an add-on feature of MAILERS+4 that comes on a separate CD-ROM.  DPV is an option found in Address Check function.  When it is enabled your list will be verified to a higher standard.  Where the CASS Certification of Address Check verifies that an address is in a valid range, DPV verifies that an actual address is valid. For example, all the addresses in the range of 120 to 130 Main St will have the same ZIP+4.  The DPV add-on will indicate which of the addresses in the range of 120 to 130 are valid or invalid and therefore should not be mailed. DPV will improve the accuracy of your mailing list and help you save on postage and printing.