I don't think there have been many discussions concerning delivery of documentation by mail and can probably highlight some issue.The document everyone is looking for will come via either in a brown innocuous envelope or a White USPS priority envelope,I say this because I almost threw it away once thinking it another credit card offer.

The issue with the address is that from now USCIS will issue all documentation and paperwork to the address given or until you update the information with them.They also don't use P.O boxes for mailing documentation so it would depend completely on the address listed.Technically,you're suppose to use the address at where you reside so how this works out for you in the future is really up to you.