I don't know what is causing your specific issue ... whether you
are getting something newer in sa-update than is designed to work with CentOS (sa-update bypasses the normal rpm type updates and does updates from elsewhere). It should only update rules, so maybe some of the new rules require a new version of perl-Net-DNS. If that is the case, then a Red Hat bugzilla entry needs to be made.
See above - it's the spamassassin restart that causes the error, in the end, nothing really to do with sa-update.
If it will not work with the CentOS version of perl-Net-DNS and if it works with the rfx version, then obviously you would run that. If that is the case, we need to get the rhel one upgraded.
So maybe I *do* need to open a bug report? Where do I do that?
can you try to disable ipv6, then reboot and see if you still get the error message?
Sorry, it's a production machine, I'd rather not do that. I can make small changes but a reboot-- Beside, if this is the set of packages CentOS gives me when I install something like spamassassin, it seems like they should work no matter what. But don't get me wrong, I really appreciate your suggestion.