block email extensions from joining

Hi

i need some help.

on my site i get a lot of membership signups which spam the blog etc from the email extension gmx.com. 

is their a way to block this extension as they dont leave an IP trace.

I am also interested in stopping those with 163.com, qq.com, sina.com etc...

I've been getting a lot of wun-hung-low@yahoo.com type people, along with those recent gmx.com spammers. When they join, to be able to do anything, they must select a membership level otherwise they default as standard and cannot post blogs or anything except limited looking. They're either incredibly dumb, can't read English or are robots because they never select their membership level. So far, all I need do is delete the accounts, but it's annoying in itself.

This post might help

help-my-site-has-been-invaded-by-chinese-people.htm

well i get a lot of the beckham's relatives that dont even know their own gender and also manhattan seems to do a lot of traveling as it has been in chigaco, washington, cincinnatti and even 1 had it in france.