When I owned a retail store, I had a twist on a mailing list. I had customer cards. If they spent so much a month, I would "punch" their card. After all the months were punched they would get a gift certificate (just before Christmas generally).
Anyway, to sign up for the card, they needed to provide specific contact information (name, address, phone, email, etc.). If they provided me with an email, I gave them an extra chance each month to opt in for a giveaway. It gave me a chance to email an advertisement of upcoming sales, customer card specials, etc. (the winner was listed in that email ad). It was one of the best marketing venues I had.
Pam
