The USPS instituted the following rules regarding Z4CHANGE Option processing:
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You must initially run your entire mailing list through CASS-certified software.
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Subsequently, it is sufficient to use Z4CHANGE Option processing on that list to maintain its compliance with CASS rules.
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You must run the entire file again at the end of the third year following initial Z4CHANGE Option certification. (This means that you do not need to run the file through CASS-certified software every year, as long as you are using Z4CHANGE Option processing.)
Note: If the USPS determines that significant changes were made to the CASS requirements, you must reprocess your entire list using recently-certified software.