Does anyone with the card recall how the card was delivered, via which service and how big the envelope was?

My card was returned to sender. Chase can't tell me why or provide a tracking number or even let me know what carrier was used so I can ask my building's concierge why it might have been refused. They say it "likely" would have been delivered by USPS in a plain regular sized envelope, but if that's the case there's no reason it would have been returned to sender. I'm only at my place in the US sporadically so would like to strategize such that the 2nd attempt doesn't also get returned.