Just because postal regulations permit them to be mailed does not preclude other reasons why that action might be illegal or expose you to legal liability.
There are lots of actions that are legal in isolation that become illegal when you do them to other people, particularly when done with malice.
Digging up my residential address or sharing it with other businesses for any purpose other than to render services (e.g. to send a package that I ordered, you might need to share it with FedEx) is harrassment IMO.
There are lots of actions that are legal in isolation that become illegal when you do them to other people, particularly when done with malice.