Banea Dominios

Creating logic for banning specific email domains.
`.info` domains, or even `.mobi`, are not-so-strange, although I doubt that spammers use them...
And there are also longer sTLD (sponsored) domains: `.moda`, `.viajes`, `.gratis`... http://www.1and1.es/nuevas-terminaciones-dominios

[DISC] I suggest not allowing nothing with less than 4 characters, and allow things with 4-6 characters only if there is a dot in the middle
 + That will prevent including any non-sponsored top-level domain, and most of the sTLDs
 + That will prevent also short strings, which can easily be part of a longer one
 - if a fucking idiot registers `idiot.com`, `idiot.org` and so, they need to be banned one by one (but hey, that's not so hard)