I completely agree! I implemented Hashcash a couple years ago into my email wrapper and the algorithm is (in it's essence) suprisingly similar to Bitcoin: given

I completely agree! I implemented Hashcash a couple years ago into my email wrapper and the algorithm is (in it's essence) suprisingly similar to Bitcoin: given this data, find a hash that has a consecutive number of x zeros in it. I don't know about the 1/20th of a second though. Back in the day, the slowest Hashcash stamp with 5 ending zeros I could produce (with optimized code of course) was marginally above 1 second. But the good thing about Hashcash is that, much like Bitcoin - the difficulty scales. Just ask for more zeroes and it'll take longer. Email clients could also use the number of zeroes to help email classification: 0 zeros = SPAM, 5-8 zeroes = HAM.