Priority or Express mail. FedEx or UPS can also send documents. The idea is to bypass the normal mail room as much as possible and to get the thing on the desk of someone who is not limited by stupid rules.
Which is particularly effective in this day and age when many businesses don’t handle a lot of incoming physics mail —- send a FedEx to a particular individual at a particular location and it is not like they have a ‘mailroom’ that handles this routinely, it is a non-routine event that somebody shows up at the front desk to deliver something and inherently memorable.