Dear boRg,
After some tests, that's what we have:
1 - If you simply set the user as not active and this user tries to log in, he will be able to resend his activation email and will also be able to activate his account.
2 - If you set the user as not active and ban his e-mail account, it's just the same. I think banning works only to new registrations, right?
3 - If you set the user as not active and he tries to use his original activation e-mail, his account will not be reactivated! That's exactly what you said.
When I say that I banned the user, I'm talking about banning his e-mail address. I can't ban his IP because of dinamic IPs and I have not found any other kind of banning -- like banning a username.
That's it for now. I think we must really change the e-mail address of the "banned" user in order to avoid his account reactivation.