I'd say the retail box is not suitable. It's not made to be an exterior box for shipping, only to be boxed up in a real shipping box.
An ESD bag, wrapping or spacers that prevent the drive from moving within its box, and a box suitable for shipping are standard requirements even if this is a return of a failed drive. The drive has to be returned in a condition that it can be evaluated and refurbished if possible, and if they can find a way to claim it was damaged due to improper packing and shipping, they can deny your return.
When you don't have original packaging, the standard way to ship a drive is like this from Western Digital's RMA instructions: