Take the rural-route and box numbers to a United States Post Office; you will need the town, state and zip code as well. The USPS can look it up and see if there is any record of an address, and if it has been changed. It can also tell you if the rural route has been changed.
Contact the 911 center of the town in which the address is located. For example, if the address is located in Brookings, South Dakota, you would contact the 911 center in Brookings for help with a rural-route number. Do not call 911 directly, but instead find the center's office numbers on its Web page.
Find a computer program that will convert the address for you; LACSLink System is suggested by the USPS. Contact your local US Post Office to learn about purchasing this software. It is a good investment if you have several rural-route addresses -- such as client files -- that you need to convert to physical addresses.