We found that there are multiple types of spammers. The quick strike individuals will register, then immediately blast a bunch of posts. Limiting day one posts can minimize their success.

But, we found another group that I call the "investor". We would find hundreds of registered users who never posted anything. They would have unimaginative user names such as 'qwerty', 'asdfg', 'zxcvb', etc. At first we simply ignored these users, but we found that they would show up months later and drop their load. From time to time one of us would go through the user base and remove or block these "investments". These were serious "investors" because full registration required replying to an email. We could also see the half registered users who failed to reply to the email.