Definition of delivery sequence file (DSF)

computerized listing, updated every two months, of all addresses served by the U.S. Postal Service. The DSF has over 125 million records. The USPS issues a limited number of nonexclusive licenses (currently nine) to private sector service companies that use the file to provide large volume mailers with list services. These services include address validation and standardization that improve address hygiene, carrier walk sequence coding, application of nine-digit ZIP codes and carrier route coding, and identification of seasonal addresses. These services increase the deliverability of the mailer's list by identifying undeliverable addresses and reduce the expense of mailing undeliverable pieces. The DSF can also be used to sort business addresses from residential. DSF does not provide corporate mail stops; the internal mail boxes many larger companies require for mailroom delivery.