Tarpits deter impatient spammers

Tarpits deter impatient spammers
Tarpits deter impatient spammers 

By Cara Garretson
Network World

CAMBRIDGE, MASS. -- Researchers have learned that spammers are impatient 
people, and theyre figuring out ways to exploit that characteristic to 
block unwanted e-mail.

Two presenters at the MIT Spam Conference 2007 held here last Friday are 
examining ways to significantly cut back on the amount of spam received 
by tricking spammers into believing theyve been caught in an SMTP tarpit 
and forcing them to disconnect before the unwanted messages have been 

An SMTP tarpit is used to catch spammers by slowing down the responses 
that the receiving mail server sends back to the sender who is 
attempting to connect and send mail. Because spammers typically blast 
out unwanted messages in bulk and have many connections to make, waiting 
for slow ones can mean lost dollars and they will usually disconnect 
rather than wait for responses, said Tobias Eggendorfer, a researcher 
with the University of Munich in Germany.

However, this approach to catching spam would mean that anyone trying to 
send e-mail to an organization using an SMTP tarpit would have an 
equally slow experience, making it an untenable option for most 
companies. To overcome that obstacle, Eggendorfer developed an approach 
called SMTP tarpitting simulation that uses stuttering, which slows down 
a mail server for the first few moments of connection, then returns to 
normal speeds, he said.

Spammers are tarpit-aware; they set short time outs and start 
disconnecting soon after they believe to be caught in one," Eggendorfer 
said. But honest senders would continue to send.

The tarpit simulator Eggendorfer developed, which is implemented on an 
SMTP proxy, cuts down spam volume by 80%. It would have to be used in 
combination with other spam-catching techniques that would filter the 
remaining 20%, he said.

Whats attractive about this technique is that by forcing the spammer to 
drop the connection, organizations save on the bandwidth, storage and 
processing power needed to implement other types of spam filtering that 
require the messages to be received, Eggendorfer said.

Another presenter at the conference discussed the advantages of e-mail 
connection management. Ken Simpson, CEO of MailChannels, has developed 
software that works with any existing mail system and leverages 
reputation and behavior information about senders to allocate connection 

The theory is spammers are impatient, so if you slow them down a bit 
theyll go away, Simpson said. Most spammers will give up within 10 
seconds of establishing a connection.

MailChannels software relies on sender reputation information to decide 
which connections to throttle back, Simpson explained. You cant throttle 
everyone, so adding a good reputation component is an important part.

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