Since that IP address is hosted in the .UK, you might also check to see if you have only a few of those subscribers and see if their hostnames are similar or have MX domain names that are similar.

If you're feeling lucky, maybe one of these contacts would intercede?

http://www.softflare.com/index.php?id=9

At 18:08 1/6/2006 Friday, Francoise Becker wrote:
>The mail is going through LISTSERV on the L-Soft Guava server, then 
>sent to Gazelle at L-Soft which delivers it to some unnamed qmail 
>server at 80.253.119.74 which then sends it back to LISTSERV on Guava