most ISP's have a domain range, which generates a max number of ip# The problem is if your block the whole range, you can be blocking an entire Sevice provider and all their customers.
The email registration account setup system is by far a much better way to manage accounts.
the person abusing it looses the account and no matter if they are using a ip generator, they would have to go through the trouble on creating a new email and new account each time, which is time consuming. Eventually they give up out of frustration.
They all do ;-) Have a range, or ranges that is. No single entity has "all" of the possible IP addy's.
The email registration account setup system is by far a much better way to manage accounts.
There are a fair number of alternatives for regulating joining, and possibly separately, posting. The limitation of e-mail account alone is a weak deterrant, because e-mail addy's are easy to get. I deal with hit and runs at Yahoo forums, and eventually went to "validate new poster (based on a post, not just an addy) before permitting a post." It's manageble only because of the low traffic.