The Postal Service wants your addresses to be correct and up-to-date. We offer the following resources to help you:
Quick Service Guide 602, Addressing, gives an overview of addressing requirements, including diagrams for address placement.
Quick Service Guide 507, Ancillary Service Endorsements, describes ancillary service endorsements, the services they provide, and the associated fees. It includes a chart to help you decide which ancillary service endorsement is right for your mail.
Publication 28, Postal Addressing Standards, provides details for addressing requirements, including complete lists of directional's (e.g., NW, SW), suffixes, and acceptable address abbreviations.