In USPS Postal Addressing Standards (Publication 28 or, affectionately, "Pub28"), the USPS presents a few general guidelines for maintaining and managing address lists. Proper management of mailing lists will help ensure that addresses in your database are accurate and complete. SmartyStreets offers customers solutions that will assist with address data management. We recommend updating addresses in your list using our LiveAddress services in order to meet these maintenance recommendations:
If your curiosity has been piqued as a result of this explanation (or you're still having trouble falling asleep) you can read the full text of the publication 28 on the USPS website or in PDF format.