Recently, a noise outside my front door set my dog, Bailey, to barking. I looked out the peephole and didn’t see anyone, but when I opened the door, there was a package on the welcome mat.

“Oh,” I said aloud, “it was the postman.”

In a split second, Bailey was out the door and racing down the street to where the carrier had stopped to deliver a package to a neighbor. He was soon snarling and trying to get a good grip on the postman’s ankle.

I was mortified. And horrified. After collecting my dog and apologizing profusely, I started to wonder about what I had just witnessed. Bailey had been fine until I spoke the word “postman.”

Why? What was it about the postman that got him riled up?

So I did some research and asked some questions. Turns out, dogs’ hatred of mail carriers is not cliche, as witnessed by the thousands of attacks on carriers every year.

The prevailing theory has to do with ancient dogs that lived in the wild. Whenever an intruder wandered into their territory, it was seldom for a friendly visit.

Dogs became domesticated, but that streak of territorial defense remains strong. As such, mail carriers, UPS drivers and pizza-delivery folks are cast in the role of intruder, coming up to the house and triggering the defense mechanism in your dog.

Now, here’s the important part. These folks show up more or less regularly. The dog barks and the intruder quickly leaves. The dog claims it as a victory. He or she has driven away the bad person. Good job. Only one problem — the intruders always come back, requiring your dog to escalate its response. The dog adds in snarls to its bark, and if given the opportunity, might bite.

Dogs, being dogs, also begin to recognize the carriers’ vehicles and uniforms, so they can become fixated on those elements. Bailey apparently has also learned the words “postman” — he also reacts to “cat” and “vacuum cleaner,” two of his other arch enemies.

Although we don’t have mail delivered to our doorstep, Bailey has had experience with mail carriers who did come six days a week, and that’s probably where he’s developed his hatred of them, although dogs don’t actually hate. As Bailey sees it, he is just defending his home and family.

If your dog also has a thing against the mail carrier, you can attempt to broker a peace by having your dog greet the carrier and attempt to make friends.

Have your dog on a leash and give your carrier some treats to give your dog. Don’t attempt to do this in your front door or near it. Moving a little ways away from the door will help ease the sense that the dog needs to protect the home.

If you can’t stop your dog’s aggression toward delivery people, make sure the dog is never out without a leash.