Somewhere in that add something like the below, assuming your using a submit button to enter the information.
if ($submit) {
mail("dlampe@home.com", "Guestbook 9 Updated", "Lot 9 Guestbook Updated");
}
if that doesn't work it may be no definition of the replyto part, so change it to the below and it should work then, I think.
if ($submit) {
mail("dlampe@home.com", "Guestbook 9 Updated", "Lot 9 Guestbook Updated", From: "dlampe@home.com\nReply-To: dlampe@home.com");
}
I'm not great, so I'm not sure how much of that you need, but it SHOULD work. Of course, if the button for entering information is called "enter" for example, its ($enter) instead of ($sumbit)
Hope that helps, and works.