Can spammers reuse stamps, sending many messages for the cost of one stamp?
Since stamps are associated with a particular piece of content (as determined by its hash), a malicious user can only reuse a stolen stamp on identical content (see also Section 3.1 of our technical paper). This security guarantee makes it effectively useless for third parties to steal stamps since they would have no control over the content. A related scenario is when a user attempts to reuse a single legitimately obtained stamp to validate a single message sent to thousands of people. This is in fact considered to be acceptable behavior from the perspective of CentMail, similar to the use of blind carbon copy (bcc) for emails. Recipients are informed, however, of the number of times a message has been verified, alerting them to down-weight the value of a donation appropriately. • Will CentMail deter web applications from sending email (e.g. Evite, Facebook, LinkedIn, etc.), and hence hamper innovation? What about other legitimate bulk mail senders? We suspect that any long-term solut
