CASS™/MASS™ Certified Products Guide - All Sections Data Files Cycle O - (Expires July 31, 2028)

This document contains the certified vendors list for CASS™ and MASS™ products for Cycle O.

USPS Verification of Periodicals Advertising Percentage – Alternate Marked Copy Program

Z4 Info File

A downloadable ZIP file containing information related to the Z4 Info File

LACSLink® Developers (PDF)

This document contains a contact list of LACS^Link® developers.

LACSLink® Distributors (PDF)

This document contains the contact list of LACS^Link® distributors. 

Early Warning System (EWS002C0.ZIP)

This file is the EWS production file and is updated weekly. This file contains the Early Warning System data file for the CASS™ and MASS™ certification process.

INFORMATIONAL: USPS APIs System Maintenance (8.27.25)

USPS® Approved Manufacturers of Mailing Containers for Adult Birds

A list of contact information for adult bird container manufacturers that have been certified by USPS.

2026 Integrated Technology Promotion

The 2026 Integrated Technology Guidebook provides you with all the details you need to successfully participate in this promotion. In the Guidebook you will find information on the eligibility, information on the Mailing Promotions Portal, and more. Navigate the document via the buttons on the side to quickly access the information most relevant to you.

DELIVERY - Atlantic Area – North Carolina District Hurricane Erin - Offices Reopened