Announcements
12/26/2025
DELIVERY - Wrightwood Post Office (92397) - Temporarily Closed
Announcements
12/26/2025
DELIVERY - Lytle Creek Post Office (92358) - Temporarily Closed
Data Files
12/26/2025
Z4 Info File

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

Data Files
12/26/2025
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
12/23/2025
INFORMATIONAL - USPS APIs System Maintenance January 14, 2026
Contact Lists
12/23/2025
CASS™ Certified Products Guide: Residential Delivery Indicator Cycle O - (Expires July 31, 2028)
Contact Lists
12/23/2025
RDI™ Cycle O: Certified Products Guide (D) - (Expires July 31, 2028)

This document outlines the CASS/MASS certified vendors list for RDI™ Cycle O.

Contact Lists
12/23/2025
CASS™ Certified Products Guide: M L O C R Mailers/Users Data File Cycle O - (Expires July 31, 2028)
Contact Lists
12/23/2025
CASS™ Certified Products Guide: M L O C R Mailers/Users Cycle O - (Expires July 31, 2028)
Contact Lists
12/23/2025
CASS™ Certified Products Guide: M L O C R Service Bureaus Data File Cycle O - (Expires July 31, 2028)