John Levine wrote:
But actually, we haven't moved it, since the bad guy can use the same stamp to send multiple spams to the same victim unless the bank also cancels the stamps.
Or unless the receiving system does elementary checks for the same stamp being used multiple times. But obviously, since your main interest is convincing everyone that e-postage is impossible, you're going to assume that the receiving system is implemented without even the most blatantly obvious checks.
mathew