Well, I wouldn't do that, but we could either way:
a) send reminder mails that only stop if you delete your account to accounts with 10 or less posts if that person wan't online for a longer time range than, let's say, 3 days or so. Many players are just lurking around and don't spam everywhere, ket.
b) send an email to every member if he wants to keep his account. I think many members that just registered and never posted would delete those. We could use the "Spam-Strategy" (sending an e-mail every week or so) to really make sure those members that want to stay can stay. I wouldn't just delete all.