Some dogs bark very excitedly at the guests regardless of indoors and outdoors. Barking is a natural thing for dogs, as dogs have their alert instincts to eliminate outsiders. However, the owner must control it properly. If the owner has a strong leadership, the dog will not bark persistently because he understands that the owner will protect them even if they do not try to protect the territory.
Some dogs look happy and excited when guests come. At first glance, it may seem like fun playful behavior, but dogs express their feelings differently depending on the character of the dog. Actually they aren't welcoming the guest and trying to eliminate strangers by appealing that they are there and letting guests know that this is their territory. They just don't groan and bite.
When outdoors, dogs are subject to various stimuli. If you have a dog at the front door, he will be on the alert and bark at, for example, the delivery person.
The flow of the actions when the delivery person comes is something like this.
The delivery person comes → the dog barks → the delivery person returns after finishing the delivery
If the dog repeats this every day, he thinks that he has driven away the outsiders by barking, he thinks he is so strong that he could do it. It's a daily thing, so it's escalating more and more.
To stop him doing it, placing his house in a less stimulating place is effective, such as the back of your house. This will reduce stress as the dog does not have to be on the alert. Just changing the location will definitely reduce the dog's barking. Even if you keep your dog indoors, prepare a house indoors and make a habit of properly isolating him by putting him in it.