Forwarding to aol.com on their accounts can falsely get you listed as the headers for a forward will indicate your server rather than the original spammers server when they list something as spam in their aol account. Normally, you might want to remove aol forwarders if this happens. You can see who is forwarding to aol by running:
egrep aol.com /etc/valiases/*
This will output a list of who is doing so.