Domains are listed in the dsn.rfc-clueless.org zone based on:
Delivery status notification for failed delivery attempts are sent from a null address ("<>") which must be supported according to STD10 and its subsequent forms. Failure to accept mail from the null address could cause undue burden for other postmasters, and is eligible for listing.
Rejecting delivery status notifications is usually caused by a misconfiguration in the mail server itself rather than being domain-specific. For this reason, domains that share an MX record with another domain already listed will also be automatically listed.
RFC 2505 (Anti-Spam Recommendations) reiterates the necessity of accepting mail to the null address.
This zone was originally populated from RFC-Ignorant.org's final data set.