lammert - 4:26 am on Jul 9, 2010 (gmt 0)
Barracuda offers a SPAM firewall solution which sits in between the Internet and incoming mail servers. It is a system used by companies and maybe some ISPs as a first line SPAM defense.
I have no idea however how they fill their IP database. Maybe they use some message heuristics, but it is also possible that the database is filled with reports from users. The website of Barracuda should give you more information about their listing and de-listing procedures of IP addresses.