The National Change of Address (NCOA®) Suppress is a database file that contains people who have:
This is gathered by the Royal Mail and has around 43 million entries with about 100,000 records added every month.
When someone moves house and gets their mail redirected they are added to both NCOA® Update and NCOA® Suppress files, if the person does not agree to let third parties know their new address then they are added to the NCOA® Suppress file only. Public and private data is also used to compile a list of recently deceased. The set is also complemented by companies who contribute their returned mail to NCOA® Suppress.
Read in more detail how the NCOA Suppress and other datasets such as AddressBase Premium and Not Yet Built can be appended to your address data to improve performance.