Slow Spammers down with Hashcash

There are two main problems with spammers and email. Firstly your email gets filled with junk and makes your email less readable and more time consuming. The second is that ISPs have more trouble delivering a reliable service to you.

ISPs have a hard time identifying real mail and letting all of that through without false positives. And because we all rely on our email, false positives are tolerated less often these days.

Hashcash is a handly little tool that adds some CPU time needed to send a single email (about a second or two) when you're sending. Hashcash inserts an ID tag into the header of your email which can be allowed through at the other end.

If you're sending out a few emails a day on your desktop machine then a delay of a second or two as Hashcash does its calculations won't effect your user experience at all. And the ID tag is inside the header of your email which you don't normally see.

Spammers can use Hashcash too but if you're a spammer with a DSL account purchased with a stolen credit card then you need to send 100 000 emails down the line quickly before your stolen account gets shut down. So a delay of a second or two on each email adds up to make things very difficult.

Hashcash is supported by the current version of SpamAssassin, TMDA and CAMRAM.

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