Actually you can use a PO BOX as a pay to address. However, this is depended upon what billing software you use, we noticed. For example, if you use Office Ally, there are forms you have to complete to use a PO BOX. We moved to Ability, EASE All Payer software and they have a built in place in the additional fields section of the claim forms where we enter the PO Boxes for our clients. That works without issue. If you are paper billing, I do not believe that you can use a PO BOX. So it just depends on the format of the software and the forms. We have 3 clients right now that we send the payments to their PO BOXES, using the EASE All Payer billing software features. However, we were not able to do this before. Bottom line - check with your billing software vendor.