Forward Confirmed reverse DNS

I read this article on wikipedia: http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS.

There, I found this tool:
http://ipadmin.junkemailfilter.com/rdns.php.

In my email account, I then select a message and right-click and choose "View message source."
About the fifth line down, I see the IP address that the message was received from.
I can then plug that IP into the tool above and validate it.