Proofs to filter spam

Embodiments of proofs to filter spam are presented herein. Proofs are utilized to indicate a sender used a set amount of computer resources in sending a message in order to demonstrate the sender is not a "spammer". Varying the complexity of the proofs, or the level of resources used to send the message, will indicate to the recipient the relative likelihood the message is spam. Higher resource usage indicates that the message may not be spam, while lower resource usage increases the likelihood a message is spam. Also, if the recipient requires a higher level of proof than received, the receiver may request the sender send additional proof to verify the message is not spam.