I'd understood that it was illegal to open someone else's mail, but IMO, when a package is delivered to the workplace it depends on the rules of that workplace. In our team, mail arrives addressed to any of us or to the team, the person opening the post opens all of it and distributes it unless the letter is marked Private and Confidential. I consider it a bonus that we are allowed to have personal parcels delivered to work (since we are never at home during the day) but I usually tell the receptionist if I am expecting something, then she looks out for it.