Domains are listed in the elitist.rfc-clueless.org zone based on:
This RFC2 list lists domains whose eMail servers refuse to talk to a large number of eMail hosts, rejecting connections or refusing to transfer mail solely based on the internet protocol address of the client.
Many large, free, eMail providers have realized that providing eMail to their users is an expensive and time-consuming task. Rather than put effort into building a support staff to manage their service, they look to restrict who is allowed to talk to them and reject any user that isn't using a large-enough eMail service provider.
It is our opinion that this is contrary to the design and intentions that
created the Internet, and which encouraged the wide-spread use of electronic
mail. There are many reasons why netizens
may choose to use smaller
mail providers, or even run their own—a practice that predates the
founding of the commercial Internet.
Maintainer's note: It's questionable how useful this list is, and it is less well defined and maintained than the other lists. If you choose to use this list, please watch this page from time to time.