Ideas to prevent spam accounts

[andre-dierker]

1. Collect ip adresses from accounts marked as spamer in a seperate table/view.
   If the ip addresses repeatly create accounts we could be able to block these. this could be mybe done in a redis table? And the ip addresses could be allowed to access again after a variable time like fail2ban does that. This could be done federated beside the other spam stuff.

2. Approve accounts by mail domain (spam related)
   I would like to allow all new user but curate new users that use mail domains from a self managed list. like I want to curate all users from gmail.com, hotmail.com etc