Can I drop off USPS packages at a UPS store?
Most definitely. Personal experience, we had a driver running late so I was sent to make the pick up at his UPS store. Once I had picked up the UPS parcels, I noticed they had USPS parcels and letters to be picked up. Seeing their mail carrier had already picked up there and I still had to go by the Post Office on my route for my pickup there, they gladly accepted my offer to take the USPS items there. I think I shocked a few customers there that were still coming in. It took about 5-10 minutes to load everything up and those that had mail to drop off were told to bring it outside to me if they wanted it sent that day. The look on their faces was priceless!