Sender-side Proof-of-Work

In order for a sender to transmit mail to a recipient, it must complete a proof of work algorithm at the recipient servers configured difficulty. Once the blob has been constructed on the sender-side, the sender is to monotonically sweep the nonce field, re-hashing the blob per every change. Once the blob hashes to a value with enough leading zeros that matches the servers configured difficulty, the blob will be accepted by the server. It is mandatory for the server to also verify nonce in order to reject mail with potential deficiencies.