Abstract: A sender-side process directed to processing an electronic message destined for a recipient, comprising producing a solution to a computational problem involving at least a portion of the message. A degree of effort associated with solving the problem may be assessed. The message is further processed according to the degree of effort by determining whether the degree of effort was within a range set by the sender or the recipient and if not, the computational problem is adjusted and solved again. The message is then transmitted to a recipient, who is informed of both the problem and solution. The recipient executes a recipient side process, comprising: assessing the degree of effort associated with generation of the message based on the problem and solution; and further processing the message in accordance with the degree of effort. The degree of effort is indicative of the legitimacy of the message; e.g., is it “SPAM”.