a code made up of numbers and letters that uniquely identifies the source of that name so results can be tracked, measured, and attributed to the mailing list. Key codes enable you to make better marketing decisions based on those results. When orders arrive, it is important to capture the key code information at the time of purchase. In cases where that is not possible, a process called "match back" or "implied response attribution" can be used to match unattributed sales to the promotional efforts that caused them.