Anti-spam Hashcash Payments

Variable: spam-use-hashcash

Similar to spam-use-whitelist (see Blacklists and Whitelists), but uses hashcash tokens for whitelisting messages instead of the sender address. Messages without a hashcash payment token will be sent to the next spam-split rule. This is an explicit filter, meaning that unless a hashcash token is found, the messages are not assumed to be spam or ham.