This bug was reported automaticaly in connection with IPv6 project. Our aim is to support IPv6 in all Fedora Core packages so FC6 and RHEL5 will be ready for IPv6. This package seems to lack IPv6 support.
perl-Socket6 and perl-IO-Socket-INET6 have been included in FC6, which improves IPv6 support. Full IPv6 support is reportedly not due until upstream's 3.2.x release. (?)
spamc/spamd supports ipv6. Other parts of spam detection itself will improve in future versions.