1. A promotion system supporting a plurality of buyer computers and a plurality of seller computers, the plurality of buyer computers used by a corresponding plurality of potential buyers, the plurality of seller computers used by a corresponding plurality of sellers, the promotion system comprising: a promotion management service that stores information regarding each of the plurality of potential buyers; the promotion management service receives from the plurality of sellers via the plurality of seller computers, a plurality of promotion data related to a plurality of respective offerings of the plurality of sellers; the promotion management service presents the plurality of promotion data via at least a subset of the plurality of buyer computers; a promotion email service that, based on the stored information, sends to a subset of the plurality of potential buyers an email including at least some of the plurality of promotion data; and the promotion management service, responsive to input received via a first buyer computer of the plurality of buyer computers, communicates to the first buyer computer promotion information for storage on the first buyer computer, the promotion information to be used to support completion of a transaction at a physical seller location of one of the plurality of sellers at a later time without retrieving the promotion information from the promotion management service.