The National Change of Address (NCOA) file is sourced from Royal Mail Redirection Service. It provides the ability to identify not only the fact that the customer has moved but also offers details of where that customer has moved to. The file is built through the capture of detailed information from customers who register their move with Royal Mail. It can be used either to suppress gone-aways or to locate lost or missing customers.

The NCOA file is updated monthly and contains just over 17 million records. Details of movers date back as far as April 1994 right up to the present day. Updates number approximately 100,000 per month. Names are only removed from the file if specifically requested by the addressee.