People wanting a post office job have to pass an exam.
The ‘exam’ is a personality test*, pretty much the same one they give at Walmart and Target. The days of the old written (or computer based) proctored exam are long gone. http://www.usps.com/careers is the link to what jobs are available.
* Proctored exams are still required for maintenance craft positions including auto repair, custodial, mechanic, etc positions.