Contact Lists
09/17/2026
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.

Release Notes
09/17/2026
Informed Visibility® Mail Tracking & Reporting (IV®-MTR) Release Notes

These release notes summarize new features and enhancements implemented in deployments to the IV-MTR application.

Data Files
09/17/2026
Z4 Info File

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

Data Files
09/17/2026
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.

 

Announcements
09/16/2026
INFORMATIONAL - UPDATE - Manifest Quality (MQ) Noncompliance
Error Codes
09/16/2026
Known Issues List 9.15.2026
Release Notes
09/16/2026
USPS APIs Release Notes

For the latest updates, please review the USPS APIs Release Notes.

Fact Sheets
09/16/2026
USPS® Post Office and Blue Collection Box Location Dataset Briefing Sheet
Applications/ Forms
09/16/2026
Occupancy Trends License Agreement
Applications/ Forms
09/16/2026
USPS Population Mobility Trends License Agreement (Sample Only)