Art Pollard wrote:
That thought also crossed my mind, where only untrusted domains would be required to Hash Cash / Penny Black (either through a whitelist or domains that don't have reverse-MX information). Which makes it a bit more like the real-world concept of "friends are always welcome, strangers have to show multiple forms of ID before they get past the front door". A targeted system would make it more palatable as you're only requiring strangers to do the calculation (or any system that doesn't seem quite on the up-and-up).HashCash / Penny Black proposals suffer from one flaw that I see... they assume that there is no legitimate reason for a low-budget organization to send high volumes of e-mail. Driving up the costs for spammers also drives up the costs for things like public mailing list servers. <SNIP> It's still an interesting idea, but I'm not sure that it's practical in the real-world.
Well, it could be combined with a whitelist. Basically, the first message (the subscribe message) could be HashCash/Penny Blacked. Then the subscriber would add them to a whitelist. If the user failed to do so after a couple of days, a warning message could be sent out and if the person again didn't whitelist the mailing list, the mailing list could unsubscribe them.
Not too bad really.
-Art