The Spamhaus Project


Spamhaus Releases Exploits Block List (XBL) to Combat Illegal Spam Relaying

by The Spamhaus TeamJanuary 01, 20042 minutes reading time

London, 1 January 2004

To help stop the rising tide of spam coming from illegal 3rd party exploits, the Spamhaus Project today released the Exploits Block List (XBL), a realtime DNS-based database of IP addresses of illegal 3rd party exploits, including open proxies (HTTP, socks, AnalogX, wingate, etc), worms/viruses with built-in spam engines, and other types of trojan-horse exploits utilized by spammers.

Spam comes from two main sources; it is either sent directly from the spammer's own IP addresses, or is sent via 3rd party exploits in an effort to obfuscate the origin. The XBL is designed to sit alongside the Spamhaus Block List (SBL) which blocks incoming spam from direct spam sources.

The XBL wholly incorporates the highly-trusted CBL (Composite Block List) from and is available immediately free of charge as

The combination of SBL and XBL enables ISPs to safely reject a high volume of incoming spam outright, without needing to accept it into their mail queues for processing. This enables the use of further slower post-receipt spam filters to process a vastly reduced volume of remaining spam.

Because of the fail-safe design of DNS-based blocklists, both the SBL and the XBL provide instant feedback to the Sender in the event an incoming message is rejected, informing the Sender via the standard SMTP rejection (bounce) message of the reason the message was rejected and what to do about it. This differs from post-receipt spam filter systems which accept all email and then silently discard or route to a trash mailbox email identified as spam without the Sender knowing.

Because of the SBL's reputation for precision combined with the fail-safe design of block lists, the Spamhaus Block List was widely adopted in 2003 by major banks, airlines and industries to whom email delivery integrity is vital. In December 2003 the number of mail users protected by the SBL surpassed 200 Million. With the addition of the XBL, Spamhaus aims to provide the maximum spam blocking possible with the safest solution.

For more information see:

Help and recommended content

See below for helpful articles and recommended content