This guy is sitting outside on his lawn when he sees his neighbor (Dave) walk outside and check his mailbox.

With a confused look on his face, Dave walks back inside the house.

Five minutes later, Dave walks outside again to check his mailbox. Seeing that there is nothing in it, he walks back inside his house.

Another five minutes later, Dave comes back outside to check his mailbox.

After watching Dave check his mailbox 3 times in a row, the guy became pretty curious. When Dave started to walk back inside again, he asks, "Dave, what are you doing going in and out every five minutes to check your mailbox?"

Dave answered: "My computer keeps telling me that I've got a mail."