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One thing I really liked about SpamAssassin and how prevalent it was was that I could set hashcash on my outbound e-mails and basically eliminate the chances of

One thing I really liked about SpamAssassin and how prevalent it was was that I could set hashcash on my outbound e-mails and basically eliminate the chances of my e-mail being caught as spam. This was probably a decade ago (I've since moved to gmail), but it would take 10-60 seconds per recipient to generate the hashcash, and SpamAssassin would give those messages a large positive weight. I'm kind of surprised that it never caught on.

gst 8y ago
Is hashcash still feasible today? With botnets it shouldn't be a major problem to generate a large number of hashcash stamps. In addition, the current hashcash approach uses SHA-1 which would be trivial to speed up with GPUs or FPGAs (similar to how Bitcoin mining works). At the same time it wouldn't be possible to increase the required "price" of hashcash stamps as this would lock out users who can only use CPUs to calculate the stamp.
- linsomniac 8y ago
  That's a good question. I assumed that the hashcash benefit in SA had been tuned over the years. I had picked the largest hashcash at the time for the 10-60 seconds per recipient. Not sure what the benefit the GPU can bring is, 10x? 100x? Yes, botnets or GPUs can be used to accelerate hashcash. But the point of hashcash isn't that it can't be accelerated, it is that it increases the cost of sending each message dramatically. Most spam seems to be sent because it is just so damn cheap to send a million messages. Adding a second to each recipient is a significant cost. Of course, as we saw with car alarms and immobilizers, there are unintended consequences with things. In cars, we moved from people stealing cars in the middle of the night, to people getting confronted at gunpoint to get the keys. I wonder if increasing the cost of sending spam might just promote the highly targeted methods like catfishing or whatnot.
- rphlx 8y ago
  These days it would probably make more sense to just require a small cryptocurrency payment in place of hashcash. There are some obvious adoption and scalability issues with that but it may be workable as a prioritization mechanism.

gst 8y ago

Is hashcash still feasible today? With botnets it shouldn't be a major problem to generate a large number of hashcash stamps. In addition, the current hashcash approach uses SHA-1 which would be trivial to speed up with GPUs or FPGAs (similar to how Bitcoin mining works). At the same time it wouldn't be possible to increase the required "price" of hashcash stamps as this would lock out users who can only use CPUs to calculate the stamp.

linsomniac 8y ago
That's a good question. I assumed that the hashcash benefit in SA had been tuned over the years. I had picked the largest hashcash at the time for the 10-60 seconds per recipient. Not sure what the benefit the GPU can bring is, 10x? 100x? Yes, botnets or GPUs can be used to accelerate hashcash. But the point of hashcash isn't that it can't be accelerated, it is that it increases the cost of sending each message dramatically. Most spam seems to be sent because it is just so damn cheap to send a million messages. Adding a second to each recipient is a significant cost. Of course, as we saw with car alarms and immobilizers, there are unintended consequences with things. In cars, we moved from people stealing cars in the middle of the night, to people getting confronted at gunpoint to get the keys. I wonder if increasing the cost of sending spam might just promote the highly targeted methods like catfishing or whatnot.
rphlx 8y ago
These days it would probably make more sense to just require a small cryptocurrency payment in place of hashcash. There are some obvious adoption and scalability issues with that but it may be workable as a prioritization mechanism.