Fiveten” ( is a blacklist run by Carl Byington, who operates under the name of “510 Software Group.” This blacklist has been around for a decade now. It lists IP addresses for a large variety of reasons.

Here are the officially announced criteria (currently listed on Fiveten’s website):

  • Individual spam sources – These are generally taken from spam samples that have arrived here, and from discussions on
  • Providers of bulk emailing services that do not require a closed-loop confirmation opt-in from their customers, or that have allowed known spammers to become their clients.
  • Output servers from multi-stage open relay chains that have sent spam.
  • Single-stage open relays.
  • Networks that provide services to spammers.
  • Web servers running vulnerable versions of or other exploitable web-to-mail gateways. This may also include machines acting as smarthosts for such web servers.
  • Providers of free mail providers.
  • Systems that send virus notifications (klez, sobig, etc.) to the supposed sender. This refers to a specific type of backscattering.



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