Many dogs bark when their owner is not home, and we can only speculate why. One good explanation is that they miss their significant human and are calling them home. Your dog’s barking is rewarded every time, eventually, because you do come home. Your dog does not understand that you were coming home anyway. Dogs chasing the postie is part of our urban folklore; the reasons for this may be similar, using “doggie logic”. Consider the following sequence of events: postie threatens to impinge the pack boundary and messes with pack property (i.e. the letterbox), dog produces territorial display (hackles up, barking), postie leaves, and dog’s behaviour is rewarded. That silly postie comes AGAIN the next day and gets driven off by your dog’s ferocious display AGAIN… And once again, your dog has done its job for the pack by driving off the interloper. Will postie never learn???