IANA blocked registration of most of them under gTLDs (.COM, .NET, etc.) in 1993, on the thought they may be useful to support extensibility of the DNS down the

IANA blocked registration of most of them under gTLDs (.COM, .NET, etc.) in 1993, on the thought they may be useful to support extensibility of the DNS down the track. Country-code operators have typically followed that lead as good practice. As they were never really used for that purpose, slowly but surely they have been released into circulation. The applications by registry operators to lift the one- and two-letter domain restrictions are at http://www.icann.org/en/resources/registries/rsep http://www.icann.org/en/resources/registries/rsep