Just by telling them what's going on, you'll definitely decrease the number of people requesting to be removed from your list. A sample statement in the first email would be: "Thanks for visiting my site and requesting the xxxxx report. You might want to also check out the area real estate maps at this link to become more familiar with where properties are located. This is the first in a series of four emails over the next couple of months, each highlighting information our visitors have found valuable."
Then in each email after that, make sure that you tell them that it is the #th email in the series of four. At the end, thank them again and tell them that you'll be sending them three or four informative emails each year (see the next step).
