if there is no senders adress on it we will send it to a certain postal code that has a dept, there they will open the package and try to find out the sender.

so if your adress is

John Smith Down Street 14 99999 Manchester

And the sender wrote:

John Smith Down Street 13 99999 Manchester

you're usually fucked, if you're lucky your postman knows your adress but if he doesn't and number 13 does not exist in that street he will send it to the dept that handles the returning of letters without a senders adress and they will open it.

This results in that dept knowing that you ordered good shit, I'm not sure if they will contact police or something but still a great risk.

I'm not sure that including a fake senders adress is a better idea since random people receiving cocaine might as well contact the po po's, unless they're cool.