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Post #8 on Why Spam Filters Suck “trickle blog” series

By Desmond Liao | 2 minute read

Dealing a Blow to Spammers

ISPs have recently been getting a lot of criticism for traffic shaping P2P file sharers. While we can argue over whether this is excessive or not, they have been doing this primarily for legitimate reasons, to reduce the impact of resource hogging users on the rest of their network.

The same technique can also have a positive impact on email, SMTP traffic shaping essentially puts shackles on email’s heaviest users­ the spammers ­who have a voracious appetite for broadband capacity. Slowing down unknown senders causes the greatest harm for spammers who need to circulate their messages as quickly as possible. In fact during peak-load times, 90% of spammers go away after 10 seconds of being put in the slow lane.

Using traffic shaping, senders of spam are literally restricted from delivering packets to the network. This slowing down approach works by shaping the TCP connection and implements in a way similar to that of a network load-balancing device.

Unlike other traffic based spam protection, traffic shaping is not about putting limits on the quantity of emails from a sender (spammers can get around this easily by sending fewer emails per zombie). In comparison, true “shaping” literally slows down suspicious email delivery to a trickle (like 3 kbps) — effectively stopping spam from flooding in and eliminating processing delays. Then senders with good reputation can be dispatched on a fast connection and given higher service priority.

The result is a clean mail stream of less than 25 per cent its original volume.

NEXT: Post #9 Real World Scenarios
PREVIOUS: Post #7 Slowing Things Down

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