On which holidays do we NOT mail out certificates via USPS?

Answer: B — Christmas Day

Certificates are not mailed out via USPS on Christmas Day because it is a federal holiday when postal services are entirely suspended. As a result, no mail, including certificates, will be dispatched on that day. Other holidays, like Thanksgiving Day, Labor Day, and Memorial Day, may have limited services but typically still allow for mail collection and delivery for various postal operations. Therefore, Christmas Day stands out as the only holiday on which certificate mailing is completely halted.