Returned letters, assignement contract, and residential status

[David White]

I have a 3 questions. My first question is what does it mean when you get a returned letter from a direct mail campaign and what do I do with the returned addresses? Also where can I find an assignment contract? Lastly I've come across properties that I deemed vacant. When I look up the property address and mailing address its the same address but under principle residence it says no. Should I send them a letter?