Anti-spam activists test mail relays and, if they find them open and without restriction, they add them to a list for server administrators to avoid. Closing open mail relays is seen as a key method of blocking spam. Activists interviewed by Wired suggest a 90% reduction in spam because the senders, without use of open mail relays, would be forced to use more costly and more traceable alternatives.
A New Zealander, Alan Brown, was recently forced by court order to close down his web site, orbs.org, that made available such a list. It followed action in New Zealand by companies aggrieved at having their servers included in the list. However, other sites have made the list of around 94,000 servers available, including one in Basingstoke, England, called Open Relay Block Zone, which states:
"ORB UK publishes a list of machines which, based on evidence held by ORB UK, are Open SMTP Relays which have, or are likely to be, used as conduits for sending unsolicited bulk email. By publishing this list, ORB UK allows system administrators to choose to accept or deny email exchange with these servers. ORB UK also separately lists machines that cannot be tested after being demonstrably open relays able to be used for Third Party Relay."