Paper on Hashcash viability

As the mail-list discussion has raised a number of interesting points,
here's a link to a paper I wrote last year which might be of interest;

http://www.payback.ie/jh/Trusted_email_using_Hashcash.pdf
"Trusted Email using Hashcash - Email spam is a growing problem; current
anti-spam techniques do little to minimise the volumes. Would a new approach
such as Hashcash proof-of-work prove a viable and universal standalone
solution?"

The research method I used involved spammer breakeven (profitability)
calculations mapped against Hashcash stamp bit-size. I've also done some
analysis on requirements of an anti-spam solution, and categorised existing
approaches to the spam problem. Including a broader look at policy/trust
proposals.

This is not a rebuttal to 'proves not to work', but takes a different
approach to the analysis.

John.