lammert - 7:40 am on Jul 13, 2010 (gmt 0)

AOL will be primarily looking at the last email server which processed the message before it was delivered to AOL, which is the IPv4 address. But some anti-spam algorithms--but I don't know AOL is using such an algorithm--also check the addresses if intermediate servers to see if an open relay or other abusable server was used in the transit of that particular message.

Such an open-relay check may choke on an IPv6 address if the routine wasn't written with IPv6 in mind.