Where can I mail my NC plates , no longer living in Nc??

The worst place ever

I would agree.. without the receipt it most likely doesn't matter. I too still have an old plate. I believe it's only going to matter if they're not out of date but the Raliegh address is 1100 New Bern Avenue

I personally have had many plates that I never returned that expired and never had a problem on future visits to the DMV. You could mail it to the main office in Raleigh but without a receipt you're probably wasting your time.