The script is supposed to work like that. It records every visit.1) I've placed it on a site that requires a visitor to use the main index page a lot in order to navigate around the site (i.e. when a visitor clicks to go to another page, if they then want to view a different page they have to click "home" and go back to the index page in order to select a new link.
Each time a visitor returns to the index page, I am sent another email stating that they visited the site. So, if someone stayed on the site for a while and returned to the index page a dozen times, I would receive a dozen emails informing me that they had visited.
Sorry I couldnt understand what you mean by this "Because I have used this email address as the email address to which the ipsniffer sends a notification, I also receive an autoreply from the email address".2) When someone visits the site and uses a contact page to send an email, the email address has an autoreply that thanks them for making contact etc. Because I have used this email address as the email address to which the ipsniffer sends a notification, I also receive an autoreply from the email address.