It would filter out most of it, but there are people who will blow way too much money on a botnet, DDoS-ing a major company because they got banned for hacking or even just because their main got nerfed, so i'm sure someone would pay for multiple email addresses just to troll an internet forum.
I'd like to know how many accounts we introduce that actively post new threads though. Maybe a manual aproval process wouldn't be so unfeasible depending on that. Account aproval itself is already a manual process AFAICT right? It would basically be an extension to that.