Check this blog at the first. We've modified our problem selection process. Now you can use this form to submit ideas. If you submitted a problem on Ninja-Setters, send it again through this form, I can't access Ninja-Setters anymore.
Still, we're in need of approximation problems (although it doesn't mean we don't need other problems), please submit them if you have any.
If you have questions, please send an email to me (firstname.lastname@example.org) or ask in comments. Please do not message me here.