I am a mail carrier. (I guess I used to be a mailperson, before things got way too PC!!)
Dinsdales idea is what they teach us. Every day Fido barks, we leave. Fido feels responsible. It can cause a problem.
I feel the need to point out that not all dogs hate the carrier. I have several who pout if I don’t open the truck door and let them in for pets and loves.
As for the dog in the OP, maybe that dog just didn’t like that person. It happens all the time and usually no one can figure out why.
And for everyone else with a carrier hateing dog, make a big deal out of talking and visiting with your carrier, with the dog safely confined. Make sure the dog knows that the carrier is someone you like and that you don’t like him barking. Try shaking hands with the carrier and letting the dog smell you. Since most dogs want to please, they should figure it out pretty quickly.
Here is my dog/mailman story. The front door to my house has a slot in it for the mail rather than a box out side. So everyday the mailman slips the mail in and my roomies dog will atatck the mail as it comes through the door. This dog has been known to bite all the way through magazines usually MY magazines. So if I’m home while the mailman comes I’ll try to get to the door so the dogs can’t get the mail. The mail man is used to me opening the door and he knows the dogs are just loud. One day the dogs start barking and spinning in circles like idiots so I know the mailman is near. When I pulled the door open…oops…not the regular mailman some new guy that had just jumped up and back about 3 ft. and looked to be in the middle of a heart attack. As soon as he was gone I had to laugh, the look on his face just killed me.
From all appearances our dog had not and aggressive bone in her body, but since we have a new baby we’ve been home during the day and noticed her ferocious response to the mailman.
I came up with the ‘Dinsdale sprinkled with pkbites’ theory a while ago, and I’m glad that I’m not alone in it.
I was a temp carrier for a short while. I had never been afraid of dogs. In fact, I could get some dogs to like me more than they liked their owners. So I don’t completely buy the smell of fear theory, not in every case. I was attacked three times on my first day. If I hadn’t had a trainer with me, the first one would have sent me to the hospital, he was really aiming for the throat. After that I figured it was the odor of the mail. Some of the letters came from the other side of the planet and that has to smell weird to the dogs, plus I was approaching the house in a way no one normally did. We were taught to cut across yards as much as possible. The direction of the approach itself could be seen as a threat. And if they aren’t watching, we appeared to pop up out of nowhere. That’s a threat to anyone.
Ok, since we are getting some good theories about this problem, try this one.
My dog will bark up a storm and jump on the door at the mail lady when I am home. But she says they are friends if I am not there and doesn’t bark at all.
You ought to read the short story “Roog” by Phil K. Dick. It describes a similar scenario from the point of view of the dog. Every week, once a week, the dirty, smelly Roogs come and steal all the valuable food his master stores in the metal cans out by the curb. So every week, just before they arrive, the dog starts howling “Roog! Roog!” but his master does not understand the warning.
Just read a great book called Why do dogs do what they do?
Including the wonderful chapter: Why do dogs sniff butts?
It claims they are being territorial, and when the mailman leaves, they’ve succeeded.
Cecil Adams on color perception among dogs (and, as a free bonus, cats).
I would think it is because the mailman comes to your door, and makes a racket. The only reason I would think this is because my dog ONLY barks at emter men, mailmen, those kinds of people. Neighborhood kids, and other people, no.
Payne N. Diaz, welcome to the boards! 
I laughed when I read your anecdote. A dog feeling compelled to PROTECT the mail carrier. Hmmm. Did your father bribe this dog in some way, or did he just display frustration at all these crazy dogs who wouldn’t let him do his job so that that dog would take pity on him and help him out?
dragonlady, you’ve got a point. I guess Shnookums didn’t like the mail lady as a person, but she’s never before snapped at our guests. As far as chatting up the mail carrier, we have. The second mail lady I mentioned, the one that Shnookums ran next door to try to bite, my mom talks to her all the time–She did so before the incident as well as after–while Shnookums locked up in the house can watch her from the window.
As you can see, it didn’t help.
ninja_rydr, interesting. I wonder what made your rommie’s dog attack the mail and yours in particular? [sigh] Dogs are just fascinating creatures that I just can’t figure out.
Thanks for sharing your experiences, nonsequitur, you’ve confirmed for me that I never, ever want to be a mail carrier.
deb2world, perhaps your dog’s just putting on a show of protecting you from the mail lady when you’re home. When you’re away, that’s when she plays. 
Thanks ChasE and vanilla. I’ll see if I can’t find the story and the book you suggested.
Thanks for the link, manhattan.
I’m just loving these stories about folks’ dogs.
That’s similar to what I’ve heard. The dog probably initally barks because a stranger is coming onto his property. The mail carrier leaves after delivering the mail, and the dog feels that he successfully scared the carrier away. Every time after, the dog barks because he knows he can easily scare off the carrier. As to why it’s so popular for dogs to bark at mail carriers, can anyone think of other strangers who come so close to a person’s house day after day? There would probably be the same effect if, say, a football player came to your door every day. It’s just more noticeable with the mail carrier, I suppose, because he visits the house on a daily basis.
Beats me but all I know is that my dogs will attack anything that moves
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