With the introduction of IPv6 in SmarterMail 11.x, there are a few security and spam checks included within SmarterMail that are exclusively IPv4 based. Below is a list of what is compatible with IPv6 from a security and anti-spam perspective.
All anti-virus measures within SmarterMail work with IPv6
SpamAssassin-based Pattern Matching
IP-based Checks Disabled for IPv6
Other Checks Disabled for IPv6
Black and White Lists
DOS and Brute Force Intrusion Detection