As soaplady said, certified can be sent to a PO box - you don't necessarily need a physical address.
I can't speak for Continental, but my office uses a PO Box for good reason.... Being in a not-so-good part of the city, our post office stinks. I've had customers mail stuff to our physical address and it seriously takes 2 weeks or more for our post office to deliver it. On the contrary, we have a PO Box in the next town over, and have never had problems getting mail there. So I always tell my customers to mail payments/correspondence to our PO Box not the physical, we will get it a lot quicker.