When Movable Type (or any other blogging software) sends a TrackBack ping, the server's IP address from which the ping was sent usually matches the IP address of the domain that is listed in the TrackBack URL.

On the other hand, when spammers send TrackBack pings, they tend to spam with many different TrackBack URLs, none of whose domains match the sending IP address.

This test will check the TrackBack ping IP address and the IP address of the domain listed in the URL to see if they match or are at least close, indicating that they might be on an associated server.

Recommended settings

On one hand, spammers almost never send TrackBack pings from the same IP address as the domains listed in the TrackBack URL so this is a great way to catch TrackBack spam. However, there is a downside: Pings sent directly from desktop blogging clients will also match the criteria for this test.

We consider this collateral damage since, in our experience, very few false positives result, while a massive number of junk TrackBacks are easily caught with this test. We recommend this test be turned on with a score weighting of 1.

If you are unsure, just make sure to check your Junk folder periodically to see if legitimate TrackBacks from your users are being incorrectly marked as Junk. You can always use the Lookup whitelist to make exceptions if the number of users affected is small.