Are there hidden costs to using CentMail?
Again, the vast majority of users who already make charitable contributions incur no additional monetary expense. Furthermore, there is also no significant computational expense (e.g., spent CPU cycles) or significant human expense (e.g., time spent solving CAPTCHAs). The system does require users to open a CentMail account and, in some cases, to install a simple application. With support from large email providers (e.g., Yahoo!, Google and Microsoft), however, this barrier to entry can be significantly reduced. • 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 singl
