Patent ID: 7921173

Claim:
In a sending domain that is network connectable to one or more receiving domains, the sending domain including a sending messaging server configured to send electronic messages to the receiving domains, a method for indicating to a receiving domain that the sending messaging server expended computational resources to solve a predetermined computational puzzle before sending an electronic message to the receiving domain, the method comprising: an act of the sending messaging server receiving electronic message data that is to be contained in an electronic message sent from the sending messaging server to the receiving domain; an act of the sending messaging server generating puzzle input from one or more components of the electronic message; an act of the sending messaging server identifying an answer document by applying a hashing algorithm to different answer documents until the hashing algorithm produces an answer hash value that is a solution to the predetermined computational puzzle, wherein the answer hash value is calculated by hashing a combination of the puzzle input and at least one of the different answer documents; and an act of sending the electronic message from the sending messaging server to the receiving domain, wherein the electronic message includes the identified answer document and the electronic message data enabling verification by the receiving domain that the sending messaging server expended computational resources without further communication with the sending messaging server.