1. A method, the method comprising by computer apparatus: matching a selected electronic message to one of multiple clusters of electronic messages transmitted between physical network nodes to convey product purchase information to designated recipients, each cluster being associated with a respective grammar defining an arrangement of structural elements of electronic messages in the cluster; segmenting the selected electronic message into tokens comprising product purchase information; parsing the tokens in accordance with the grammar associated with the cluster matched to the selected electronic message, wherein the parsing comprises identifying ones of the tokens that correspond to respective ones of the structural elements defined in the grammar and extracting unidentified ones of the tokens as field tokens; determining classification features of the selected electronic message; classifying respective ones of the extracted field tokens with respective product purchase relevant labels based on respective ones of the determined features; and in non-transitory computer-readable memory, storing associations between the product purchase relevant labels and the product purchase information corresponding to the respective ones of the extracted field tokens in one or more data structures permitting computer-based generation of actionable purchase history information.