Updated February 21, 2007
TrackBack is a feature of Movable Type (and Typepad) that allows you to let other sites know that you have linked to them, and lets you know when other sites have linked to you.
If enabled, the TrackBack feature will place a direct link on your Movable Type entry to entries from other sites that are linking to your entry. Conversely, if you place a link on your weblog entry that links to another site's entry, a link to your site will show up on the other site's entry.
Why is TrackBack useful?
1. It's kind of cool to see that other people are thinking well enough of what you have written on your weblog to actually link to it.
2. It allows you to comment on someone else's entry without actually having to make a comment in their comment field. If you think well enough of what they wrote to write about it on your own weblog, you don't have to leave a comment on their site in order to let them know you are writing about them.
Why is TrackBack problematic?
1. If you allow TrackBack on your weblog, you are letting anyone place a link to their site on to your blog. This capability has been abused by spammers (see ahead to the TrackBack Spam section).
2. If you allow TrackBack links, you will need to do more site maintenance to remove TrackBack links that are no longer valid. Otherwise, your site will be filled with links to 404 error pages, which can reduce your ranking with the search engines.
How to enable TrackBack
TrackBack only works if both sites that are being referenced (either you are referencing another site or another site is referencing you) have TrackBack enabled. To enable TrackBack from your end, go to Settings > Feedback in your blog's settings. Select Accept Trackbacks.
You can hold Trackbacks for approval before they post, and be sent an email when a Trackback has been attempted.
If you want to send a Trackback to another site, you can specify Trackback URLs to ping on an individual entry case-by-case basis. Near the bottom of the edit entry screen for each entry is a links that says Customize the display of this page. Click on that link to select the Editor fields you want displayed. Select Outbound Trackback URLs. In the Outbound Trackback URL field of the Entry Edit page you can place another site's entry's Trackback URL.
You can usually find a specific TrackBack URL for someone else's weblog entry by scrolling to the bottom of the entry. If they have TrackBack enabled, you'll find the TrackBack URL that you can copy and paste into your URLs to Ping window. If you cannot find a reference to TrackBack on someone's entry, they probably do not have TrackBack enabled, and therefore you would not be able to ping them using TrackBack.
Similar to comment spam, spammers have found a way to abuse Movable Type's TrackBack feature. They ping your weblog entry's trackback, even though they have nothing to do with your entry, they just want a link back to their website showing up on yours. There are several measures you can take to counteract Trackback spam. See the LMT tutorial Trackback Spam for details.
TrackBack Timeout Error Messages
When sending pings, Movable Type sets a timeout on the amount of time it takes to send the ping, so that the system doesn't appear to freeze up. The default timeout time is 15 seconds. If the ping takes longer than that, you'll get a timeout error message.
You can adjust the timeout period by going into the mt-config.cgi file on your server, un-commenting (removing the # at the beginning of the line) the PingTimeout line and changing the number in that line to a larger number of seconds.
# PingTimeout 15