I don't know about how it is in the us, but as far as for germany any domain inside the TLD "de" must have at least three literals.

So any domain name as aa.de to zz.de would be valid according to naming conventions, but never have been registered and never will be, so there are no DNS records for them. Ok, once one knows about those country specific details all parser would check for such limitations as well. But anyway, what is the worth of a "spammers mail list spammer" if the use of EMAIL::Valid and Co. will assure that such a list would be clean?

Have a nice day
All decision is left to your taste