This is mainly a simple little redirector for <mail id> -> mail gateway. It's primarily used in kernel development and kernel change logs.

If you are seeing this, you are doing it wrong. The syntax for using this is:

http://lkml.kernel.org/r/<message-id> - for marc.info links
http://lkml.kernel.org/g/<message-id> - for gmane.org mail-archive.com links