Hi, I just registered here but immediatly hit a problem. I could not use my main account "@gmx.de" and I don't know why. GMX is the or one of the biggest freemail provider in germany. If you would say "we ban all free mails because spam" okay but you allow gmail which is the same (but different, but still same).
So I would suggest you to remove it from your blacklist since there is nothing more spamy about it compared to any other freemail provider