“P. O. box AT THE POST OFFICE” ~ that’s what you said. Then you concluded that it had to be taken by an employee.
You get a failing grade in reading comprehension. Let's look at what I said:
"When I was 13, my grandmother made the mistake of sending me $100 by first-class mail for my birthday, instead of mailing me a check. When the envelope got to me, it had been opened and re-taped, and there was no money in it. I think I know what happened to it though. Some drug addict obviously broke into the post office and took the money. It wasn't anyone who worked for USPS."
I didn't mention a P.O. box. I don't know the intricacies of how mail delivery works, but I'm assuming that when it gets to my local post office, it is sorted before being given to the mail carrier. Am I right in assuming that? So what I was saying is that a postal employee somewhere in the chain must have removed the money from the envelope. It could have been the mailman (unlikely), or it could have been someone like a mail sorter at either my grandmother's local post office or at my local post office.
No, I am the one who was ripped off by a postal employee from my postal box. And the way it’s laid out, no one could possibly do things as you suggested, not without being noticed by someone working there.