If you use Mail::SpamAssassin and the default configuration, and have enabled the default relay checks but disabled bayes testing, or you have tweaked your configuration so that you enabled the checks for Osirusoft under additional circumstances, you should take steps immediately to disable such checks. Apparently, after having been DDOS'ed, the Osirusoft people have "given up the ghost" and are now returning back every IP as a spam source when queried!

I've added this to my ~/.spamassassin/user_prefs:

score RCVD_IN_OSIRUSOFT_COM 0.0
score X_OSIRU_DUL 0.0
score X_OSIRU_DUL_FH 0.0
score X_OSIRU_OPEN_RELAY 0.0
score X_OSIRU_SPAMWARE_SITE 0.0
score X_OSIRU_SPAM_SRC 0.0
[download]

I suggest you do the same. If you manage SpamAssassin for a site rather than a personal delivery, you'll need to add similar lines to the site-wide configuration.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

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update - added RCVD... line based on feedback from slashdot posting