Anti-spam blacklist service, The Open Relay Database (ORDB), has pulled the plug after five and a half years because of spammers’ growing sophistication.

ORDB was designed to deal with a technique in which spammers used SMTP proxy servers to flood the internet with junk email. The project distributed a blacklist of mail servers that allowed third-party relay — “open relays” — and were thus liable to be used by spammers.

But the list had levelled off at around 225,000 over the past year and updates have slowed to a crawl, the volunteer-run project acknowledged. “It’s been a case of a long goodbye as very little work has gone into maintaining ORDB for a while,” organizers said in a message this week on the project’s website. “The general consensus within the team is that open relay RBLs (Real-time Blackhole Lists) are no longer the most effective way of preventing spam from entering your network.”