1 Trillion RBL Requests

McFadden Associates says it's publicly available Realtime DNS Black List has handled over 1 trillion - that's 1,000,000,000,000 requests from e-mail filters.

A Realtime Black List (or RBL) takes queries in the form of DNS requests. It's sent a DNS address to resolve - such as mailserver.imaspammer.com. It then returns an answer in the form of an IP address - such as 127.0.0.3. Different IP addresses can have different meanings - but usually any sort of answer besides 'not found' indicates bad news.

The RBL is most commonly accessed by software as opposed to end-users. Most commonly they're used by server-side to block spam email. Recently, client-side anti-spam clients have started using RBL's also.

RBL's are most commonly used to diagnose if a mail server is likely to be the source of spam. Some RBL's also are used to reject all traffic due to hacker related activity, or excessive open proxy servers.

McFadden's servers typically tag about 15% of email as being from suspect sources.

SpamButcher's spam killer can optionally be configured to use an RBL of the user's choice. By default it's not enabled.

RBL's can provide valuable information in helping to determine if a message is spam or not. However, there have been some problems with RBL providers shutting down their servers without notice and "ungracefully". In at least a few of these circumstances junk mail blocker software deleted millions of legitimate email messages.

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