Maybe if it's just a bot - why not create a "login forum" ? Every new member just can post there and all new threads are sent to Moderation Queue. Maybe an open thread with something like "I read & understood the gpsundeground rules" and once such a reply has been made upgrading people from the "login" group to the real "members" group.
If it's a human - it helped sometimes contacting Google and other search engines giving them the links complaining about a manual link farm that they remove it from their index. If it's some auction site - complain there.
Might help a little bit
Or in this case - the mail providers They tend to be even more "aggressive" when their service is abused for spam
Thanks for your suggestions guys.
About report link. We have report button under every post and thread. The two black cards are icon of reporting. You can use it to report any post and our staff will take action on it immediately.
About spamming, this is not spam from bots. As bots can't process our registration process. We will implement block user to start thread before X number of post. So we can avoid this issue to..
In the end thanks for your valuable suggestions and interest in our community.