sprints.... the part that makes it "technically against the rules" (always loved that term... sorta like being "technically pregnant"... but I digress...) is the prescription that the recipient enter the note into the system FIRST, before spending it or passing it on. It generates a "hit" that did not occur "naturally" (here defined as the unencumbered/unconditional flow of currency).

By the bye... you CAN exchange and thus receive snail mail from other trackers WITHOUT it containing a tracked note -- it used be called "penpals"! :)