Why should people send spam to invalid addresses?
Because the spammer doesn’t have a nice list of valid email accounts to send to, they guess account names at known domains. Sometimes even the domain is guessed. These guesses may be proper names or they may be random combinations of letters and numbers. These emails go out by the million! Occasionally the spammer hits a vaild email account, those emails will get delivered, the rest will be rejected by the mail server.
