It wouldn’t surprise me if one slipped through, there are overrides on stuff that get rejected and USPS is a massive organization with millions of parcels moving at any given moment.

This idea came from people mailing wooden shims back to the credit card companies because it would increase the postage cost over the normal weight… Please don’t do that though. Letters go through a Dr. Seuss Esque sorter system and the shims are too sturdy and sometimes get ripped out of the mail and shot across the facility…