Post office box locks are standard five pin tumbler cylinders that can be easily bumped open, even though they have a restricted and protected keyway. Unfortunately the keys and locks can be purchased on eBay because they are surplussed out at closed military bases. Marc Tobias conducted an in-depth analysis of locks by USPS and by UPS Mail Boxes. These locks are not secure and as demonstrated in the video, can be quickly opened by bumping with an easy-to-produce blank.
Watch the special report on KELO-TV Sioux Falls about security and post office boxes.
Download the video file from this report: KELO-TV VIDEO RE BUMPING 040406