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I used to have a long long set of firewall rules that prevented inbound SMTP connections from "notorious" spammer networks, mostly in Asia. At some point I realized that nearly all my spam comes straight to my machine from zombie machines all over the place (thanks to the lucrative and prolific SanCash operations). When all your spam is for King Replica Watches or VPXL, you figure that some spam control measures are working and others aren't.

Perhaps this is not news to anyone. But over the weekend I took the drastic step of changing those firewall rules to allow inbound SMTP from a very small set of networks and refuse all other SMTP. This has worked, with only one piece of spam arriving in the last 36 hours. And my "spam-smtp" firewall chain is only 7 rules long now instead of 519.

Most of my mail should be inbound from the campus main relay and redirection systems anyway, which have a sophisticated and aggressive spam filtering/rejection feature of their own that works pretty well. But if you've been using my specific machine address instead of using netid redirection, you probably won't be able to reach me, now.

The overarching problem is that with no central control over the Internet, authenticated exchange of email is impossible to implement, and large providers are loathe to take intermediate steps with SMTP-AUTH because it's "too hard" for the end user. I think the only answer to this will be to eventually abandon SMTP altogether; a new mail distribution architecture could easily be designed from the ground up and since it would be relatively free from mass spam, should prove to be commercially viable.


( 1 comment — Comment )
Oct. 6th, 2008 11:43 pm (UTC)
I've a feeling that we may have to go for one of those systems where the sender hosts the actual message. Though, then you have to make sure the notification channel ("I have a new mail for you, it is hosted at this URL") isn't easy to spam.

Not sure if it would be enough to make this hosting-URL contain a hash of the sender and recipient addresses and a date, so that you have to host a seperate URL for each (sender, recipient, date) triple. At least your mail system could automatically 'remove' those from your inbox if the hosting URL went away, as opposed to the present-day botnet zombies that only have to live for the smtp transaction.
( 1 comment — Comment )



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