IPv6 and Spam filtering

I came across this article today talking about issues with IPv6 and email. The main issue talked about was reverse look-ups. Reverse look-ups could be dangerous if an attacker can "command (a very large number of IP addresses), they can fill your cache really fast." The article further goes on to say that most spam filter reputation systems don't yet support IPv6 and could cause problems with blocking spam based off reputation. The article suggests "if you use IPv6 reputation systems, don’t look up the data over DNS to arrange for a zone transfer."

The article can be found here
http://www.itworldcanada.com/news/e-mail-and-ipv6-what-it-admins-need-to-know/143080