Mixed SMTP-IP Level Tarpits
A server can determine that a given mail message is spam, e.g. because it was addressed to a spam trap, or after trusted users' reports. The server may decide that the IP address responsible for submitting the message deserves tarpitting. Cross-checking against available DNSBLs can help avoiding to include innocent forwarders in the tarpit database. A daemon exploiting Linux libipq can then check the remote address of incoming SMTP connections against that database. SpamCannibal is a GPL software designed around this idea; Stockade is a similar project implemented using FreeBSD ipfirewall.
One advantage of tarpitting at the IP level is that regular TCP connections handled by an MTA are stateful. That is, although the MTA doesn't use much CPU while it sleeps, it still uses the amount of memory required to hold the state of each connection. On the opposite, LaBrea-style tarpitting is stateless, thus gaining the advantage of a reduced cost against the spammer's box. However, it has to be noted that making use of botnets, spammers can externalize most of their computer-resource costs.
Read more about this topic: Tarpit (networking)
Famous quotes containing the words mixed and/or level:
“It seems to me that our three basic needs, for food and security and love, are so mixed and mingled and entwined that we cannot straightly think of one without the others. So it happens that when I write of hunger, I am really writing about love and the hunger for it, and warmth and the love of it and the hunger for it ... and then the warmth and richness and fine reality of hunger satisfied ... and it is all one.”
—M.F.K. Fisher (b. 1908)
“It is only for a little while, only occasionally, methinks, that we want a garden. Surely a good man need not be at the labor to level a hill for the sake of a prospect, or raise fruits and flowers, and construct floating islands, for the sake of a paradise. He enjoys better prospects than lie behind any hill. Where an angel travels it will be paradise all the way, but where Satan travels it will be burning marl and cinders.”
—Henry David Thoreau (1817–1862)