I am administering a public web forum based on Invision Power Board v2.3.6. Registrations are already filtered thanks to ReCaptcha, but I still have loads of people that seems to register manually to actually post 1 or 2 spams and never look back.
Validating the registration upfront does not seem very tractable because I can distinguish between regular users and spammers.
The ideal solution would be to put newly registered users on probation to let them freely post, but to keep the posts invisible as long they have not been manually validated.
Then, the manual validation would directly upgrade genuine posters as regular users (posts being directly visible, no moderation).
IPB provides a complex policy system, I think such scheme (or something equivalent) is possible. Any ideas on this matter?
Create a group called "Less than 1" all freshly registered users fall into this group. Set that user group to promote to regular "member" after 1 post. Create a forum and make this forum the ONLY forum that the "Less than 1" group can see. Hide this forum from the rest of the masses so only your super mods and admins can see it. That way when they make their first post which will probably be spam you will be able to see it and delete the user with the rest of your users being none the wiser.
There is a website that has a bunch of information to help you eliminate forum spam... www.stopforumspam.com, They have registered lists of known spammers that is kept very up to date (updates hourly). I implemented this on my sites and my spam went from 40+ incidents a day to only 1 incident in the last month or two. They even have an API for access to the data so you don't have to download the data list all the time. And it's a free service.
I'd see if there is a module available for your software that links in with them.