Check out Dan Kennedy for some killer stuff on Direct Mail campaigns.
The more you mail your list the more responses you will get, got to build the relationship. Don't just expect to send once and have people buy. It's like asking for marriage on the first date.
Make the content really interesting and relevant to them and you can charge people to sign up for your list. Then send the content out to everyone even if they didn't choose to pay (helps cover costs and your still marketing to everyone).
The fastest way to follow up your real estate internet leads Follow Up Boss