Name servers MUST be able to load all RR types except MD and MF from configuration files. The MD and MF types are obsolete and MUST NOT be implemented; in particular, name servers MUST NOT load these types from configuration files.
The RR types MB, MG, MR, NULL, MINFO and RP are considered experimental, and applications that use the DNS cannot expect these RR types to be supported by most domains. Furthermore these types are subject to redefinition.
The TXT and WKS RR types have not been widely used by Internet sites; as a result, an application cannot rely on the the existence of a TXT or WKS RR in most domains.