I'm not a postman, but a sub-contract courier.....like a fedex guy. I'm not really as fat as 'newman' but I've got the gut of a transport worker. 
I get the same greeting newman does. 
Ahh I see. That's a shame that people would treat you that way. Whenever I receive a package, I always treat the courier with the respect he deserves and make sure to let him know that I value the work he does to ensure the safe and speedy arrival of my parcel.
Maybe you could give 'em a good affirmative action people or muzzie joke with each package, that sure as hell would brighten my day!