According to the usual news sites (e.g. Slashdot), the old ORDB spam blacklist (closed in 2006) now returns false positives for all queries. This is rather nasty, since mail systems still using it now mark all checked mails as spam. Depending on the configuration, this either rejects or at least sorts out all incoming mails. This does not only relate to mail servers, but also to all kind of client-side spam filter plugins and tools. Old versions of Spamassassin are a good candidate.

The Heise article explains that this is intended as some kind of wakeup call, in order to reduce the still high amount of useless queries. Deleting the domain is argued to be a non-valid solution, since the load then goes to the .org name servers. This is really the strange part of the argumentation, since it completely ignores the DNS negative response caching mechanisms (see RFC 1034, section 4.3.4, and RFC 2308, or here). They are part of Bind since 1996.