Most often, it is just your dog’s instinct to protect his home and family from trespassers. A dog considers humans and other dogs as its own kind, so unknown members of these species are viewed with suspicion. So, when the mail carrier comes up to the door, your dog instinctively barks and/or chases. The mail carrier retreats. The dog who started barking simply because someone was there now believes that his courageous barking frightened away the delivery person. He doesn’t understand that the mail carrier would have left anyway to continue his rounds. So he’ll exhibit the same behavior the next time the mail carrier comes.
Once the mail carrier notices the dog’s threatening behavior, he or she may begin to show discomfort with body language that the dog picks up on. A vicious cycle is in place and it can continue to other uniformed people as well.
How to ease the tension
Work with your dog on some obedience training to stop the barking. Reward calm, quiet behavior with praise, toys or treats. It can also help to bring your pet outside on a leash to meet and socialize with the mail carrier. Many mail carriers are happy to make friends with the dogs on their route and often come armed with treats.