Many candidates go off of voter registration rosters for their mailings - not just parties. Those that are sent to a particular party usually have 1 name on the address (Joe Citizen 123 Main St. Anywhere, USA) , while blanket mailings will have a general address (123 Main St. Anywhere, USA)
Within the last 30 days, I've received 65 cards in the mail, 28 phone calls, and 3 door-to-door solicitors - from both parties - telling me how I should vote. Mailings go in the shredder, phone calls get disconnected, and solicitors simply get a smile and a nod.