outlook on win xp

receiving duplicate e-mail from one client every time he sends a e-mail i get two messages from him. he tried deleting out my name from his list and then set it back up. no one else in the office is getting duplicate e-mail from this client. i checked rules and did not see anything unusuall.all of my mail is handled by cox cable and then i down load into outlook. we do not have a server in house.