Assuming you are in US. If you fill out change of address form, then USPS tells them: https://www.forbes.com/sites/adamtanner/2013/07/08/how-the-post-office-sel

Assuming you are in US. If you fill out change of address form, then USPS tells them: https://www.forbes.com/sites/adamtanner/2013/07/08/how-the-post-office-sells-your-new-address-with-anyone-who-pays-and-the-little-known-loophole-to-opt-out/ https://www.forbes.com/sites/adamtanner/2013/07/08/how-the-p... The direct mail business has this “public records” part figured out pretty well and they gather the data from anywhere they can. Wouldn’t be surprised if utility bills factor in as well.