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The war on spam is mostly waged between spammers and ISP's, invisible to the public.

Earlier I wrote about greylisting. That's a fairly minimal change in handling email, that reduces the spam volume on our mail servers disproportionately. How can this be? Let's take a look at the economics involved.

At the NFG mail servers, we block about 10 spam messages for every valid email our customers receive. Even so, customers keep asking for more agressive spam filters.

Spam filtering requires a lot of system resources. Content filtering involves opening each message and matching its full contents against a database of spam patterns. This involves a lot of disk read/write actions and heavy number crunching.

In the graph above, our mail server was flooded with more spam than it could adequately handle. Of course, we could allocate more system resources or try and tune the server some more. However, the solution turned out to be much simpler: greylisting.

Externalities, asymmetric information, game theory, network effects, innovation diffusion: understanding the countermeasures arrayed against spam, involves a venerable catalog of analysis tools in the economics of information.

Since this is just a blog post, not a book, I'll try and keep it short and sweet.