Hi,
USPS is usually pretty good about delivering packages to the lockers, unlike UPS or FedEx that just leave them on the floor of the lobby. Are you sure it wasn't delivered to a locker?
I've had issues with packages being left, and contacted the leasing office to please put another sign saying that all packages need to be delivered to the lockers (there is a small one in the lobby, but drivers don't see it in its current location). The office said they weren't allowed to hang another sign in a more visible location, although I don't understand why. If other people are having issues, I would suggest contacting the office and asking for the sign to be moved to the front door. Maybe if enough of us ask, something will change.
-Danielle